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# Recent problems solved by 'robertb'

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 Age_Word_Problems/363485: hari is twice as old as his son. twenty years ago, he was four times as old as the son.find the present age of each1 solutions Answer 259177 by robertb(4012)   on 2010-10-29 06:27:18 (Show Source): You can put this solution on YOUR website!son = s years old, hari = 2s years old. Now 4(s-20) = 2s - 20. 4s - 80 = 2s - 20, 2s = 60, the age of hari, s = 30, the age of the son.
 Equations/363460: can you help me solve -17+t/5=31 solutions Answer 259175 by robertb(4012)   on 2010-10-29 06:24:12 (Show Source): You can put this solution on YOUR website!, , .
 Functions/363390: What advantage(s) can you see of having a function rule instead of a table of values for a function? Explain. 1 solutions Answer 259174 by robertb(4012)   on 2010-10-29 06:21:46 (Show Source): You can put this solution on YOUR website!One of the advantages is , for a function rule (like a formula or equation), the domain is bigger, and thus could be used more precisely and with more versatility to model natural phenomena. Another advantage is, if we restrict ourselves to table of values only, we cannot develop a lot of mathematics around the concept of functions.
 Coordinate-system/363472: I need help with finding the coordinates of the y-intercept and the x-intercept, in that order. 2x+y=101 solutions Answer 259173 by robertb(4012)   on 2010-10-29 06:10:46 (Show Source): You can put this solution on YOUR website! is the same as ,after division by 10. This is in intercept form. Thus the x-intercept is (5,0) and the y-intercept is (0,10).
 Miscellaneous_Word_Problems/363475: The least and greatest numbers in a list of 7 real numbers are 2 and 20 ,respectively. The median of the list is 6 , and the number 3 occurs most often in the list. which of the following could be the average (arithmetic mean) of the numbers in the list ? I 7 II 8.5 III 10 (A) I only (B)I and II only (c) I and III only (D) II and III only (E) I, II, and III 1 solutions Answer 259172 by robertb(4012)   on 2010-10-29 06:07:54 (Show Source): You can put this solution on YOUR website!(E) I, II, and III. We could have the following arrangement for the numbers: 2,3,3,6,x,y,20, in ascending order. The mean is formed as follows: . If the average is 7, then x+y = 15, which is very much possible for two numbers x and y between 6 and 20.(Take 7 and 8, e.g.) If the average is 8.5, then x+y = 25.5, which again is possible for two numbers between 6 and 20 (take 10 and 15.5, e.g.) If the average is 10, then x+y = 36, which again is possible for two numbers between 6 and 20 (take 17 and 19, e.g.)
 Probability-and-statistics/363476: if j is chosen at random from the set { 4,5.6 }and k is chosen at random from the set { 10,11,12 }. what is the probability that the product of j and k is divisible by 5 ?1 solutions Answer 259170 by robertb(4012)   on 2010-10-29 05:44:38 (Show Source): You can put this solution on YOUR website!***if j is chosen at random from the set { 4,5,6 }and k is chosen at random from the set { 10,11,12 }. what is the probability that the product of j and k is divisible by 5 ?*** The answer is 5/9. Just form the "multiplication table" for j and k. The possible products are 40,50,60,44,55,66,48,60,72. Out of the 9 products, 5 are divisible by 5. Hence the answer.
 Rational-functions/363481: The speed of train A is 20mph slower than the speed of train B. Train A travels 230 miles in the same it takes train B to travel 330 miles. Find the speed of each train.1 solutions Answer 259169 by robertb(4012)   on 2010-10-29 05:37:22 (Show Source): You can put this solution on YOUR website!, , , , A = 46 mi/hr, the speed of train A, A + 20 = 66 mi/hr, the speed of train B.
 Rational-functions/363482: Jack usually mows his lawn in 4 hours. Marilyn can mow the same yard in 6 hours. How much time would it take for them to mow the lawn together.1 solutions Answer 259168 by robertb(4012)   on 2010-10-29 05:32:35 (Show Source): You can put this solution on YOUR website!, , , or x = 2.4 hours, the time it would take them to mow the lawn together.
 Probability-and-statistics/363454: A random experiment has sample space S ={a, b, c}. Suppose that P[{a, c}] = 5/8 and P[{b, c}] = 7/8. Use the axioms of probability to find the probabilities of elementary events. 1 solutions Answer 259154 by robertb(4012)   on 2010-10-29 01:17:00 (Show Source): You can put this solution on YOUR website!P[{a,b,c}] = P[{a,c}] + P[{b,c}] - P[{c}]. Thus - P[{c}]. Hence P[{c}] = 1/2. Now P[{a,c}] = P[{a}] + P[{c}], so P[{a}] = 1/8. Finally, P[{b}] = .
 Probability-and-statistics/363430: In Texas 75% of all drivers wear their seat belts. A) Out of 160 drivers, what is the expected number who are wearing their seat belts? B) How many drivers will need to be observed in order to be 99.5% certain of observing more than two wearing their seat belts? Thank you in advance.1 solutions Answer 259153 by robertb(4012)   on 2010-10-29 01:00:03 (Show Source): You can put this solution on YOUR website!A) B)We have to solve the equation . The closest value of n that would work for this is n = 8: .
 Systems-of-equations/363440: 4.2z=-4(0.6z-1.8)1 solutions Answer 259152 by robertb(4012)   on 2010-10-29 00:32:54 (Show Source): You can put this solution on YOUR website!, , ,
 test/363369: Here is question: find the sum of all multiples of 4 that are between 14 and 523. Thank for help me1 solutions Answer 259098 by robertb(4012)   on 2010-10-28 21:28:33 (Show Source): You can put this solution on YOUR website!a1 = 16 and an = 520. Also, an = a1 + (n-1)d = 16 + (n-1)4 = 4n + 12. We solve for n. 520 = 4n + 12. 4n = 508, or n = 127. By the formula for the sum of an arithmetic series, .
 Mixture_Word_Problems/363371: Find the cost per ounce of a sunscreen made from 120 oz of lotion that cost \$3.42 per ounce and 80 oz of lotion that cost \$11.37 per ounce1 solutions Answer 259095 by robertb(4012)   on 2010-10-28 21:18:17 (Show Source): You can put this solution on YOUR website!\$/oz.
 Probability-and-statistics/363372: A recent study of cardiovascular risk factors reports that 30% of adults meet the criteria for hypertension. If 15 adults are assessed, what is the probability that: a. Exactly 5 meet the criteria for hypertension? b. None meet the criteria for hypertension? c. Less than or equal to 7 meet the criteria for hypertension?1 solutions Answer 259089 by robertb(4012)   on 2010-10-28 21:11:00 (Show Source): You can put this solution on YOUR website!a. , to 5 decimal places. b. c. +...+
 Mixture_Word_Problems/363358: A metallurgist needs to make 12.4 lb of an alloy containing 50% gold. He is going to melt and combine one metal that is 60% gold with another metal that is 40% gold. How much of each should he use?1 solutions Answer 259078 by robertb(4012)   on 2010-10-28 20:53:11 (Show Source): You can put this solution on YOUR website!0.60x + 0.40(12.4 - x) = 0.50*12.4, 0.60x + 4.96 - 0.40x = 6.2, 0.20x = 1.24, x = 6.2. He has to mix 6.2 lb of the 60% gold alloy, and the same amount of the 40% gold alloy.
 Points-lines-and-rays/363362: The equation c=\$.05m+ \$ 4.95 represents the cost (C) of a long didtance telephone call of m minutes. what is the slope of the line? what does the slope represent in this situation? what is the y-intercept (C-intercept)? what does the y-intercept represent in this situation?1 solutions Answer 259072 by robertb(4012)   on 2010-10-28 20:47:57 (Show Source): You can put this solution on YOUR website!The slope of the line is is 0.05. It means that every minute of call costs a nickel. The c-intercept is 4.95, and it means the fixed cost of making a call: you pay \$4.95 whether you make a call or not.
 Rational-functions/363333: 4x(x-6)-5x(x-5)=-21 solutions Answer 259055 by robertb(4012)   on 2010-10-28 20:30:14 (Show Source): You can put this solution on YOUR website!, , , or , . Hence x = 2 or x = -1.
 Exponents-negative-and-fractional/363350: what percent of 75 is 27? 1 solutions Answer 259054 by robertb(4012)   on 2010-10-28 20:27:12 (Show Source): You can put this solution on YOUR website!27/75 = 0.36. Thus 27 is 36% of 75.
 Linear-equations/363351: equation of a line containing the given point and perpendicular to the given line: (4,-3);2x+7y=81 solutions Answer 259050 by robertb(4012)   on 2010-10-28 20:21:30 (Show Source): You can put this solution on YOUR website!The desired equation would have the form , where c is a constant that is to be determined. To find c, plug in the coordinates of the given point into the desired equation: 7*4 - 2*-3 = c, or 28 + 6 = c, or c = 34. Therefore the eqaution is .
 Rectangles/363339: The perimeter of a rectangle is 30 inches, and its area is 36 in2. Find its length and width. 1 solutions Answer 259049 by robertb(4012)   on 2010-10-28 20:15:31 (Show Source): You can put this solution on YOUR website!2l +2w = 30, or l+w = 15. we have l = 15 - w. Also, area is lw = 36. By direct substitution, (15 - w)w = 36. , , , w = 3 or w = 12. The rectangle is 3"x 12".
 Expressions-with-variables/363347: Solve for C: P = R-C/n I'm stuck. I can get as far as this: Pn = R-C Pn-R = -C I'm stuck getting rid of the negative to solve for C. Please help!1 solutions Answer 259045 by robertb(4012)   on 2010-10-28 20:11:45 (Show Source): You can put this solution on YOUR website!, , after transposing terms. , after cross-multiplication by n.
 Polynomials-and-rational-expressions/363341: can you please explain the steps identify the polynomial as a monomial, trinomial, or none of these give its degree and leading coefficient -35w^9+12w^4-2w^2+9 the ^ symbol means to the power of thank you1 solutions Answer 259042 by robertb(4012)   on 2010-10-28 20:09:27 (Show Source): You can put this solution on YOUR website!None of the above. It's just a polynomial with 4 terms. The degree of the polynomial is 9, and the leading coefficient is -35.
 Mixture_Word_Problems/363297: What quantity of 70 percent acid solution must be mixed with a 20 percent solution to produce 900 mL of a 50 percent solution?1 solutions Answer 259041 by robertb(4012)   on 2010-10-28 20:01:53 (Show Source): You can put this solution on YOUR website!, , , mL, the amount of 70% solution that must be added.
 Polynomials-and-rational-expressions/363343: can you please explain the steps identify the ploynomial as a monomial, binomial,or none of these give its degree and leading coefficient -5x+8 thank you1 solutions Answer 259040 by robertb(4012)   on 2010-10-28 19:57:49 (Show Source): You can put this solution on YOUR website!The expression is an example of a BINOMIAL, or a polynomial with 2 terms. The degree is 1 (the highest power of x in the equation), and the leading coefficient is -5 (the coefficient of x.)
 Distributive-associative-commutative-properties/363340: what properties are used in the following questions: 1. 3+[a+(-a)]=3+0 2. 3+[a+0]=3+a1 solutions Answer 259039 by robertb(4012)   on 2010-10-28 19:55:33 (Show Source): You can put this solution on YOUR website!1. additive inverse property, 2. additive identity property.
 Numbers_Word_Problems/363268: find a number such that 18 more than 4 times the sum of the number and -19 is 26.1 solutions Answer 259038 by robertb(4012)   on 2010-10-28 19:53:21 (Show Source): You can put this solution on YOUR website!4(n + (-19))+18 = 26, 4(n-19) = 8, 4n - 76 = 8 4n = 84, n = 84/4 = 21.
 Graphs/363316: Determine whether the two lines are parallel, perpendicular, or neither; 3y + 21= 2x 2y= 16-3x1 solutions Answer 259037 by robertb(4012)   on 2010-10-28 19:49:24 (Show Source): You can put this solution on YOUR website!The two lines are perpendicular: the slope of the top equation is 2/3, while the slope of the bottom eqaution is -3/2. The product of the slopes is -1, and hence the conclusion.
 Rectangles/363317: the perimeter of a square is 4x-8. Express the length of one side of the square in terms of x.1 solutions Answer 259036 by robertb(4012)   on 2010-10-28 19:46:48 (Show Source): You can put this solution on YOUR website!If the perimeter is 4x-8, then the measure of each side is just one-fourth of this: x-2.
 Travel_Word_Problems/363320: how do i do the problem b=rt r= 55 m/p t= 8.25h1 solutions Answer 259035 by robertb(4012)   on 2010-10-28 19:45:09 (Show Source): You can put this solution on YOUR website!Maybe you meant d = rt? If r = 55mi/hr and t = 8.25 hr, then d = (55 mi/hr)*(8.25 hr) = 453.75 mi.
 Graphs/363329: how do you graph y=5+10x1 solutions Answer 259034 by robertb(4012)   on 2010-10-28 19:41:15 (Show Source): You can put this solution on YOUR website!Since the graph is a straight line, just find two points satisfying the equation and draw a straight line through them: (0,5) and (-0.5, 0) are two points that satisfy the equation.