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nerdybill answered: 6960 problems
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Answer 216483 by nerdybill(6962) on 2010-05-08 01:38:00 (Show Source):
You can put this solution on YOUR website!
.
From inspection, we see that the function describes a parabola that opens downwards. As such, finding the axis of symmetry will give us our answer.
.
The axis of symmetry is found by:
x = -b/2a
x = -144/(2*(-16))
x = 144/(2*(16))
x = 72/16
x = 4.5 seconds
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Miscellaneous_Word_Problems/301757: A certain species of bacteria in a laboratory begins with 200 cells and has a half life every 20 minutes. How many cells of the bacteria will be left after 1 hour (60 minutes)? Write an equation to model the problem and then solve your equation for the given value. 1 solutions
Answer 216378 by nerdybill(6962) on 2010-05-07 16:56:19 (Show Source):
You can put this solution on YOUR website! A certain species of bacteria in a laboratory begins with 200 cells and has a half life every 20 minutes. How many cells of the bacteria will be left after 1 hour (60 minutes)? Write an equation to model the problem and then solve your equation for the given value.
.
Use the exponential growth/decay formula:

Where
P(t) is amount after t time
Po is the initial amount
r is the rate of growth/decay
t is time
.
Using the first sentence we can determine r:
(1/2)(200) = 200e^(r*20)
1/2 = e^(r*20)
ln(.5) = r*20
ln(.5)/20 = r
-.03466 = r
.
Our equation then is:

Now, we can answer:
How many cells of the bacteria will be left after 1 hour (60 minutes)?

25 cells left after 60 minutes
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Rate-of-work-word-problems/301708: I have a problem but cannot figure out the equation (formnula) necessary to find the answer. All the examples I can find give me the rates but not the total time, but this one is the opposite.
Working together, Jenny and Natalie can mop a warehouse in 5.14 hours. Had she done it alone it would have taken Natalie 12 hours. How long would it take Jenny to do it alone?
Thank you for your help.
Jonathan 1 solutions
Answer 216318 by nerdybill(6962) on 2010-05-07 12:12:05 (Show Source):
You can put this solution on YOUR website!Working together, Jenny and Natalie can mop a warehouse in 5.14 hours. Had she done it alone it would have taken Natalie 12 hours. How long would it take Jenny to do it alone?
.
Let x = number of hours if Jenny worked alone
then
5.14(1/x + 1/12) = 1
Multiplying both sides by 12x we have:
5.14(12 + x) = 12x
61.68 + 5.14x = 12x
61.68 = 6.86x
9 hours = x
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Quadratic_Equations/301613: The height of a ball in feet is modeled as f(x)=-16x^2+96x, where x is the time in seconds after it is hit. How long is the ball in the air? 1 solutions
Answer 216254 by nerdybill(6962) on 2010-05-07 00:30:47 (Show Source):
You can put this solution on YOUR website!The height of a ball in feet is modeled as f(x)=-16x^2+96x, where x is the time in seconds after it is hit. How long is the ball in the air?
.
The time it is in the air is equivalent to the time it hits the ground -- so, set f(x) to 0 and solve for t:
f(x)=-16x^2+96x
0=-16x^2+96x
0=16x^2-96x
0=x^2-6x
0=x(x-6)
x = {0,6}
Solution: 6 seconds
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Rate-of-work-word-problems/301609: Barney can build a barn in 15 hours. david can build a barn in 10 hours. How long will it take for the barn to be built if they work together? 1 solutions
Answer 216253 by nerdybill(6962) on 2010-05-07 00:27:47 (Show Source):
You can put this solution on YOUR website! Barney can build a barn in 15 hours. david can build a barn in 10 hours. How long will it take for the barn to be built if they work together?
.
Barney's rate: 1/15
David's rate: 1/10
.
Let t = time it takes for both
then
t(1/15 + 1/10) = 1
Multiply both sides by 150:
t(10 + 15) = 150
25t = 150
t = 6 hours
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Exponential-and-logarithmic-functions/301569: Carbon-14 has a half-life of 5700 yrs. Scientists use this fact to determine the age of things made of organic material. Suppose the average page of a book containing approximately 0.5 mg of carbon-14 is put into a time capsule. How much c-14 will each page contain after 5700 yrs. 1 solutions
Answer 216221 by nerdybill(6962) on 2010-05-06 22:23:52 (Show Source):
You can put this solution on YOUR website!Carbon-14 has a half-life of 5700 yrs. Scientists use this fact to determine the age of things made of organic material. Suppose the average page of a book containing approximately 0.5 mg of carbon-14 is put into a time capsule. How much c-14 will each page contain after 5700 yrs.
.
Since 5700 years is the "half-life" exactly
0.25 mg will remain.
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logarithm/301576: how long will it take for the population of a certain country to triple if its annual growth rate is 2.8%? (round to the nearest year.) Use this exponontial growth model P(t) = P0ekt 1 solutions
Answer 216218 by nerdybill(6962) on 2010-05-06 22:15:28 (Show Source):
You can put this solution on YOUR website!how long will it take for the population of a certain country to triple if its annual growth rate is 2.8%? (round to the nearest year.) Use this exponontial growth model P(t) = P0ekt
.

Let x = initial population
then

Dividing both sides by x:

39 years = t
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Money_Word_Problems/301425: How long does it take $1,150 to double if it is invested at 9% interest compounded monthly? Round your answer to the nearest tenth. 1 solutions
Answer 216150 by nerdybill(6962) on 2010-05-06 18:03:56 (Show Source):
You can put this solution on YOUR website! How long does it take $1,150 to double if it is invested at 9% interest compounded monthly? Round your answer to the nearest tenth.
.
Compound interest formula:
Regular Compound Interest Formula

.
P = principal amount (the initial amount you borrow or deposit)
r = annual rate of interest (as a decimal)
t = number of years the amount is deposited or borrowed for.
A = amount of money accumulated after n years, including interest.
n = number of times the interest is compounded per year
.

7.7 years = t
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Functions/301455: (3,5);x+8y=9
Write an equation of the line containing the given point and parallel to the given line. Express your answer in the form y=mx+b. This is my problem. I have serious difficulties trying to solve these types of equations. This is for Algebra 1 in Axia College online degree program. 1 solutions
Answer 216143 by nerdybill(6962) on 2010-05-06 17:49:08 (Show Source):
You can put this solution on YOUR website!(3,5);x+8y=9
.
First, we find the slope of:
x+8y=9
Do this by putting it into the "slope-intercept" form:
y = mx +b
where
m is the slope
.
x+8y=9
8y= -x+9
y = (-1/8)x + 9/8
From above, we know our new line has
slope of -1/8
and it crosses:
(3,5)
.
Plug the above data into the "point-slope" form:
y - y1 = m(x - x1)
y - 5 = (-1/8)(x - 3)
y - 5 = (-1/8)x + 3/8
y = (-1/8)x + 3/8 + 5
y = (-1/8)x + 3/8 + 40/8
y = (-1/8)x + 43/8 (this is what they're looking for)
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logarithm/301264: 2log(x^2+4x)=1
Professor says there are two answers? 1 solutions
Answer 216008 by nerdybill(6962) on 2010-05-06 09:11:16 (Show Source):
You can put this solution on YOUR website!2log(x^2+4x)=1
log(x^2+4x)^2=1
(x^2+4x)^2=10^1
(x^2+4x)^2=10
x^2+4x=sqrt(10)
x^2+4x-sqrt(10) = 0
x^2+4x-3.162 = 0
Using the quadratic formula we get:
x={0.676, -4.676}
.
Details of quadratic:
| Solved by pluggable solver: SOLVE quadratic equation with variable |
Quadratic equation (in our case ) has the following solutons:

For these solutions to exist, the discriminant should not be a negative number.
First, we need to compute the discriminant : .
Discriminant d=28.6491106406735 is greater than zero. That means that there are two solutions: .


Quadratic expression can be factored:

Again, the answer is: 0.676243198995259, -4.67624319899526.
Here's your graph:
 |
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Finance/301265: Ten liters of a 4% acid solution must be mixed with a 10% solution to get a 6% solution. How many liters of the 10% solution are needed? 1 solutions
Answer 216003 by nerdybill(6962) on 2010-05-06 09:01:28 (Show Source):
You can put this solution on YOUR website! Ten liters of a 4% acid solution must be mixed with a 10% solution to get a 6% solution. How many liters of the 10% solution are needed?
.
Let x = liters of 10% solution needed
then
.04(10) + .10x = .06(10+x)
.4 + .10x = .6+.06x
.4 + .04x = .6
.04x = .2
x = 5 liters
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Reduction-of-unit-multipliers/301249: how do I find how many hours it took to make 3510 products when it took only 36 minutes to make 1. whats the conversion please
many thanks
Kay 1 solutions
Answer 216002 by nerdybill(6962) on 2010-05-06 08:58:41 (Show Source):
You can put this solution on YOUR website!how do I find how many hours it took to make 3510 products when it took only 36 minutes to make 1.
.
Since it takes 36 minutes for each:
36*3510 = 126360 minutes
.
Converting to hours:
126360/60 = 2106 hours
.
Converting to days:
2106/24 = 87.75 days
or
87 days and 18 hours
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Miscellaneous_Word_Problems/301267: A picture 19 inches by 24 inches is to be mounted on a piece of matboard so that there is an even amount of mat all around the picture. How wide will the border be if the area of the border is 188 square inches? 1 solutions
Answer 215999 by nerdybill(6962) on 2010-05-06 08:42:23 (Show Source):
You can put this solution on YOUR website! A picture 19 inches by 24 inches is to be mounted on a piece of matboard so that there is an even amount of mat all around the picture. How wide will the border be if the area of the border is 188 square inches?
.
Let w = width of border
then
"area of border" = "area of mat" - "area of picture"
188 = (19+2w)(24+2w) - 19(24)
188 = 456+38w+48w+4w^2 - 456
188 = 38w+48w+4w^2
188 = 4w^2+86w
0 = 4w^2+86w-188
0 = 2w^2+43w-94
Solve using the quadratic formula. Doing so yields:
w = {2, -23.5}
Of course, we can toss out the negative solution leaving:
w = 2 inches
.
Details of quadratic:
| Solved by pluggable solver: SOLVE quadratic equation with variable |
Quadratic equation (in our case ) has the following solutons:

For these solutions to exist, the discriminant should not be a negative number.
First, we need to compute the discriminant : .
Discriminant d=2601 is greater than zero. That means that there are two solutions: .


Quadratic expression can be factored:

Again, the answer is: 2, -23.5.
Here's your graph:
 |
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Quadratic_Equations/301003: Quadratic application
If the cost ,C(x) for manufactoring x units of a certain product is given by
C(x)=x^2-125x+50, find thye units manufactored at a cost of $9500 1 solutions
Answer 215865 by nerdybill(6962) on 2010-05-05 18:35:20 (Show Source):
You can put this solution on YOUR website!If the cost ,C(x) for manufactoring x units of a certain product is given by
C(x)=x^2-125x+50, find thye units manufactored at a cost of $9500
.
The given quadratic:
C(x)=x^2-125x+50
where
C(x) is the cost
x is the number of units
.
Simply plug in the given cost and solve for x:
C(x)=x^2-125x+50
9500 = x^2-125x+50
0 = x^2-125x-9450
Apply the quadratic formula when then yields:
x = {178.07, -53.07}
.
Throw out the negative solution leaving:
x = 178 units
.
Details of quadratic formula follows:
| Solved by pluggable solver: SOLVE quadratic equation with variable |
Quadratic equation (in our case ) has the following solutons:

For these solutions to exist, the discriminant should not be a negative number.
First, we need to compute the discriminant : .
Discriminant d=53425 is greater than zero. That means that there are two solutions: .


Quadratic expression can be factored:

Again, the answer is: 178.069243313262, -53.0692433132622.
Here's your graph:
 |
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Pythagorean-theorem/300752: Two planes take off from an airport at the same time. They fly at right angles to each other and one hour later they are 390km apart. If one plane travels 210km/hr faster than the other, what is the speed of the two planes?
I tried to apply Pythagoras Theorem, making the hypotenuse 390, and the sides x and x+210. I squared 390 = the sum of the squares of x and x+210, but my answers always come out wrong. 1 solutions
Answer 215727 by nerdybill(6962) on 2010-05-05 06:10:41 (Show Source):
You can put this solution on YOUR website!Two planes take off from an airport at the same time. They fly at right angles to each other and one hour later they are 390km apart. If one plane travels 210km/hr faster than the other, what is the speed of the two planes?
.
Let x = speed of slower plane
then
x+210 = speed of faster plane
.
x^2 + (x+210)^2 = 390^2
x^2 + (x+210)(x+210) = 390^2
x^2 + x^2+420x+44100 = 152100
2x^2+420x+44100 = 152100
x^2+210x+22050 = 76050
x^2+210x-54000 = 0
(x+360)(x-150) = 0
x={150, -360}
Throw out the negative:
x = 150 km/hr (slower plane)
.
faster plane:
x+210 = 150+210 = 360 km/hr
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Miscellaneous_Word_Problems/300724: bill has a collection of 65 nickels and dimes. their total worth is $5.50. find how many nickels and dimes bill has 1 solutions
Answer 215720 by nerdybill(6962) on 2010-05-05 01:24:14 (Show Source):
You can put this solution on YOUR website! bill has a collection of 65 nickels and dimes. their total worth is $5.50. find how many nickels and dimes bill has
.
Let n = number of nickels
then
65-n = number of dimes
.
.05n + .10(65-n) = 5.50
.05n + 6.5 - .10n = 5.50
6.5 - .05n = 5.50
-.05n = -1
n = 20 (number of nickels)
.
number of dimes:
65-n = 65-20 = 45
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Rectangles/300727: The area of a square is 5 more times than its perimeter. Find the length of a side. 1 solutions
Answer 215719 by nerdybill(6962) on 2010-05-05 01:20:55 (Show Source):
You can put this solution on YOUR website! The area of a square is 5 times than its perimeter. Find the length of a side.
.
Let x = length of one side of square
then
"area of square" = "5 more times than its perimeter"
x^2 = 5(4x)
x^2 = 20x
x^2 - 20x = 0
x(x - 20) = 0
x = {0, 20}
.
length of side must be 20
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logarithm/300705: How long will it take for the population of a certain country to double if its annual growth rate is 3.5%? (Round to the nearest year) Use the exponential growth modle P(t) = poe kt 1 solutions
Answer 215717 by nerdybill(6962) on 2010-05-04 23:26:49 (Show Source):
You can put this solution on YOUR website!How long will it take for the population of a certain country to double if its annual growth rate is 3.5%? (Round to the nearest year) Use the exponential growth modle P(t) = poe kt
.
P(t) = poe^kt
.
Let x = initial population
then
2x = xe^(.035t)
dividing both sides by x:
2 = e^(.035t)
ln(2) = .035t
ln(2)/.035 = t
19.80 = t
round to nearest year:
20 years = t
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Mixture_Word_Problems/300675: To reduce 16 ounces of a 18% saline solution to a 10% solution, how much distilled water (to the nearest tenth oz.) should a nurse add?
The nurse should add ________ oz. of distilled water.
1 solutions
Answer 215693 by nerdybill(6962) on 2010-05-04 22:00:04 (Show Source):
You can put this solution on YOUR website!To reduce 16 ounces of a 18% saline solution to a 10% solution, how much distilled water (to the nearest tenth oz.) should a nurse add?
.
Let x = ounces of distilled water to add
then
.18(16) = .10(16+x)
2.88 = 1.6+.10x
1.28 = .10x
12.8 = x
.
The nurse should add 12.8 oz. of distilled water.
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Quadratic_Equations/300563: Find the dimensions of a rectangular lawn whose perimeter is 100 feet and whose area is 600 square feet.
--They want me to use the quadratic formula, but I don't know how to set the equation up. That's all I'm having trouble with. I know how to use the quadratic formula fairly well. Can you please help me?
~Thanks! 1 solutions
Answer 215647 by nerdybill(6962) on 2010-05-04 19:01:12 (Show Source):
You can put this solution on YOUR website!Find the dimensions of a rectangular lawn whose perimeter is 100 feet and whose area is 600 square feet.
.
Let x = length
and y = width
.
2(x+y) = 100 (equation 1)
xy = 600 (equation 2)
.
Solve equation 2 for y:
xy = 600
y = 600/x
.
Substitute the above into equation 1 and solve for x:
2(x+y) = 100
2(x+600/x) = 100
x+600/x = 50
x^2+600 = 50x
x^2-50x+600 = 0
(x-20)(x-30) = 0
.
x = {20,30}
.
Dimensions are 20 feet by 30 feet
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Quadratic_Equations/300547: Suppose you are going to construct a circular fish pond in your garden. You want the pond to cover an area of 300ft^2. What is the radius of the pond? 1 solutions
Answer 215645 by nerdybill(6962) on 2010-05-04 18:51:19 (Show Source):
You can put this solution on YOUR website! Suppose you are going to construct a circular fish pond in your garden. You want the pond to cover an area of 300ft^2. What is the radius of the pond?
.
Since area of a circle is
(1/2)(pi)r^2
.
300 = (1/2)(pi)r^2
300 = (1/2)(3.14)r^2
600 = (3.14)r^2
600/3.14 = r^2
191.0828 = r^2
3.72 feet = r
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logarithm/300393: How long will it take for the population of a certain country to double if its annual growth rate is 5.1%?
I have been dividing ln2 by 5.1%?
A)14 yr
B)6 yr
C) 39 yr
D) 1 yr 1 solutions
Answer 215573 by nerdybill(6962) on 2010-05-04 15:03:45 (Show Source):
You can put this solution on YOUR website!.
Apply:
A = Pe^(rt)
.
Let x = current population
then
2x = xe^(.051t)
2 = e^(.051t)
ln 2 = .051t
ln 2/.051 = t
13.6 years =t
.
Closest answer would be B
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percentage/300381: I am terrible at math, can you please help me? Thank you again.
A saleswoman is working on a 6% commission basis. If she wants to make $2,400 in one month, how much must she sell? 1 solutions
Answer 215564 by nerdybill(6962) on 2010-05-04 14:33:53 (Show Source):
You can put this solution on YOUR website!A saleswoman is working on a 6% commission basis. If she wants to make $2,400 in one month, how much must she sell?
.
Let x = amount she sells
then
.06x = 2400
x = 2400/.06
x = $40,000
She must sell $40,000 worth of merchandise
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