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Recent problems solved by 'robertb'

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Exponents/485174: (2/x) ^ (-2) 1 solutions Answer 331849 by robertb(4012)   on 2011-08-23 20:52:18 (Show Source): You can put this solution on YOUR website!

Percentage-and-ratio-word-problems/485176: if you have 20 yards of ribbon and need to cut it into 2 yard lenghts, how many cuts do you have to make 1 solutions Answer 331848 by robertb(4012)   on 2011-08-23 20:50:08 (Show Source): You can put this solution on YOUR website! 9 cuts.

Probability-and-statistics/481093: Person A and Person B are doing target practice. Person A hits the target with a probability of 0.8, while Person B hits the target with a probability of 0.9. What is the probability that Person B hit the target given that both of them fired and exactly one shot hit the target? a. 0.18 b. 0.30 c. 0.69 d. 0.90 I came up with .50*.80 =.40 and .50*.90=.45 thus .40*.45=0.18 Is this correct? Thank you 1 solutions Answer 329453 by robertb(4012)   on 2011-08-13 01:26:29 (Show Source): You can put this solution on YOUR website! If exactly one of them hits the target, then the probability is 0.80*0.10 + 0.90*0.20 = 0.26. Hence the the probability that person B hit the target given that both of them fired is , or 0.69 to 2 decimal places. c. 0.69

Probability-and-statistics/481091: The probability that event A will occur is 40%, while the probability that event B will occur is 60%. What is the probability that event A or event B will occur, if the events are indendent? a. 20% b. 24% c. 76% d. 100% Thank you . 1 solutions Answer 329452 by robertb(4012)   on 2011-08-13 01:18:08 (Show Source): You can put this solution on YOUR website! P(A or B) = P(A) + P(B) - P(A and B) = P(A) + P(B) - P(A)*P(B) = 0.40 + 0.60 - 0.40*0.60 = 0.76 c. 76%

Probability-and-statistics/481058: Consider a large population with a mean of 100 and a standard deviation of 21. A random sample of size 36 is taken from this population. The standard error of the sampling distribution of sample means is equal to: A) 16.67 B) 12.25 C) 3.50 D) 1.71 1 solutions Answer 329423 by robertb(4012)   on 2011-08-12 21:57:46 (Show Source): You can put this solution on YOUR website! C) 3.50 standard error =

Subset/481063: Two fair dice are rolled. Find the probability that the sum of the two numbers is not greater than 5. Please help me 1 solutions Answer 329422 by robertb(4012)   on 2011-08-12 21:51:27 (Show Source): You can put this solution on YOUR website! There are 10 possible outcomes: (1,1) (1,2), (2,1) (1,3), (2,2), (3,1) (1,4), (2,3), (3,2), (4,1) Hence the probability is 10/36, or 5/18.

Expressions-with-variables/481071: ax-by = a^2 + b^2 2bx - ay = 2b^2 + 3ab - a^2 Find x and y in terms of a and b?? 1 solutions Answer 329420 by robertb(4012)   on 2011-08-12 21:43:58 (Show Source): You can put this solution on YOUR website! x = = = = a+b ==> y = a - b, after substitution into the first equation.

Probability-and-statistics/479518: a plane has 2 engines, the probability of 1 engine failing in a 1 hour flight is .02, what is the probability of both engines failing? 1 solutions Answer 328586 by robertb(4012)   on 2011-08-09 04:29:32 (Show Source): You can put this solution on YOUR website! The probability of both engines failing in a 1 hour flight is 0.02*0.02 = 0.0004, assuming independence of the two engines.

Numeric_Fractions/479507: if p-n^2=x and (n+1)^2-p=y then,prove that p-xy is a perfect square. 1 solutions Answer 328584 by robertb(4012)   on 2011-08-09 04:16:54 (Show Source): You can put this solution on YOUR website! p - xy = = = = = = = = = = = = = = and the proof is complete...

Triangles/479556: two sides of an equilateral triangle have lenghts 3x + 1 and -2x+26. which of 21-x or 3x-4 could be the lenght of the third sid 1 solutions Answer 328574 by robertb(4012)   on 2011-08-09 03:07:42 (Show Source): You can put this solution on YOUR website! 21 - x. To see this, solve for 3x + 1 = -2x + 26. ==> 5x = 25, or x = 5. ==> the length of a side is 3*5 + 1 = 16. since while 21 - 5 = 16, the answer is 21 - x.

logarithm/479561: explain why y= -x+b is its own inverse 1 solutions Answer 328573 by robertb(4012)   on 2011-08-09 03:04:45 (Show Source): You can put this solution on YOUR website! Algebraically speaking, if f(x) = -x + b, then , also, because , which would satisfy the definition of an inverse function for f(x). Graphically speaking, the graph of in general is just the symmetric rotation of the graph of f(x) about the line y = x. Since the line y = -x + b is perpendicular to the line y = x, a single symmetric rotation about the line y = x would yield the same graph, meaning the inverse function must be equal to itself.

Sequences-and-series/479566: write a formula for the nth term of the infinite sequence: 5,-6/2,7/4,-1,9/16,... 1 solutions Answer 328570 by robertb(4012)   on 2011-08-09 02:56:16 (Show Source): You can put this solution on YOUR website! Should be for n = 1, 2, 3, 4, 5,... .

Exponential-and-logarithmic-functions/479085: The amount of money in an account with continuously compounded interest is given by the formula A = Pe^rt, where P is the principal, r is the annual interest rate, and t is the time in years. Calculate to the nearest tenth of a year how long it takes for an amount of money to double if interest is compounded continuously at 6.2%. 1 solutions Answer 328290 by robertb(4012)   on 2011-08-08 00:21:54 (Show Source): You can put this solution on YOUR website! The working equation would be ==> ==> ==> ==> t = 11.2 years.

Expressions-with-variables/479023: If 9 - 6x = 45 find the value of x - 4 1 solutions Answer 328289 by robertb(4012)   on 2011-08-08 00:16:44 (Show Source): You can put this solution on YOUR website! If 9 - 6x = 45, then 6x - 9 = -45 ==> 6x - 9 - 15 = -45 - 15 <==> 6x - 24 = -60 ==> 6(x-4) = -60 ==> x -4 = -10.

Probability-and-statistics/479054: In a survey, 65% of Americans said they own an answering machine. If 12 Americans are selected randomly, find the probability that at least 9 own an answering machine. 1 solutions Answer 328288 by robertb(4012)   on 2011-08-08 00:09:13 (Show Source): You can put this solution on YOUR website! to 5 decimal places.

Probability-and-statistics/479104: the temperature at 6am at a specific location is it discrete or continous? The diameter of a circular object is it discrete or continous? 1 solutions Answer 328287 by robertb(4012)   on 2011-08-08 00:02:51 (Show Source): You can put this solution on YOUR website! Both are continuous variables.

Exponential-and-logarithmic-functions/479088: Solve log(4x + 10) = 3. Round your answer to the nearest tenth. 1 solutions Answer 328286 by robertb(4012)   on 2011-08-08 00:01:37 (Show Source): You can put this solution on YOUR website! The exponential equivalent is . ==> 1000 = 4x + 10 ==> 990 = 4x ==> x = 247.5.

Rate-of-work-word-problems/479076: A can do 1/3 of certain work in 10 days and B can do 2/5 of the same work in 8 days find in how many days the work will be completed if they work together? 1 solutions Answer 328282 by robertb(4012)   on 2011-08-07 23:00:32 (Show Source): You can put this solution on YOUR website! <==> ==> x = 12 days to finish the job working together.

Rate-of-work-word-problems/479075: A can do 1/3 of certain work in 10 days and B can do 2/5 of the same work in 8 days find how much work can B do in 1 day. 1 solutions Answer 328280 by robertb(4012)   on 2011-08-07 22:58:48 (Show Source): You can put this solution on YOUR website! B can do of the work in a day.

Rate-of-work-word-problems/479073: A can do 1/3 of certain work in 10 days and B can do 2/5 of the same work in 8 days find how much work can A do in 1 day. 1 solutions Answer 328279 by robertb(4012)   on 2011-08-07 22:57:36 (Show Source): You can put this solution on YOUR website! A does 1/3 of the work in 10 days. ==> A does of the work in a day. The information about B is just to confuse you.

Rate-of-work-word-problems/479081: Four men take 3 hurs to paint a wall. How much time would 6 men take to do the same job? (Ans. 2 Hours) 1 solutions Answer 328277 by robertb(4012)   on 2011-08-07 22:51:17 (Show Source): You can put this solution on YOUR website! 1/12 = the part done by 1 man per 1 hour. or, the work requires 12 man-hours to finish the wall. Let x = # of hours to finish painting the wall ==> ==> 6x = 12 ==> x = 2 hours.

Rate-of-work-word-problems/479078: A can do a piece of work in 16 days and B can do it in 20 days. These worked together for 5 days and then B leaves in how many days will finish the semaining work. (Ans.7) 1 solutions Answer 328276 by robertb(4012)   on 2011-08-07 22:47:32 (Show Source): You can put this solution on YOUR website! <==> ==> ==> ==> 5 + A = 12 ==> A = 7 days for A to finish the remaining work.

Probability-and-statistics/479070: In a game of change if you purchase one ticket out of the 100 tickets being sold at a cost of $5.00 how much money would you expect to win taking into consideration the cost of the ticket. The winning prize is $500? If I purchase two tickets instead of one ticket at the same cost of $5.00 each, how much money would I expect to win, taking into consideration the cost of the tickets if the winning prize is $500. Which of these games, if any, are fair? 1 solutions Answer 328275 by robertb(4012)   on 2011-08-07 22:44:10 (Show Source): You can put this solution on YOUR website! let x= random variable for the earnings If only one ticket is bought, If x = -5, then p(x) = 99/100, If x = 495, then p(x) = 1/100, and so E(x) = -5*(99/100) + 495*(1/100) = 0, the expected earning. If 2 tickets are bought, E(X) = -10*(98/100) + 490*(2/100) = 0, the expected earning. Both games are fair.

Graphs/479065: solve equation |3x+5|=1 thank you 1 solutions Answer 328263 by robertb(4012)   on 2011-08-07 22:23:38 (Show Source): You can put this solution on YOUR website! ==> 3x + 5 = -1 or 3x + 5 = 1 ==> 3x = -6, or 3x = -4 ==> x = -2, or x = -4/3.

Graphs/479064: solve equation 3|3x-4|-7=5 1 solutions Answer 328262 by robertb(4012)   on 2011-08-07 22:22:23 (Show Source): You can put this solution on YOUR website! 3|3x - 4| = 12 ==> |3x - 4| = 12/3 = 4 ==> |3x - 4| = 4 ==> 3x - 4 = 4 or 3x-4 = -4 ==> 3x = 8 or 3x = 0 ==> x = 8/3 or x = 0.

Miscellaneous_Word_Problems/478993: If your electricity costs 27cents for 4 kilowatt hours, how much electricity have you used if your bill is $42.oo? 1 solutions Answer 328217 by robertb(4012)   on 2011-08-07 19:31:02 (Show Source): You can put this solution on YOUR website! The consumption rate is 27/4 = 6.75 cents/kwh. Hence the electric consumption is (4200 cents)/(6.75 cents/kwh) = 622.22 kwh

Complex_Numbers/478982: Let x and y be integers such that x+y and y/x are both odd integers. Which is true about x and y? choose the answer and explain the reason to choose your response x is prime The situation is impossible y is odd y>x 1 solutions Answer 328213 by robertb(4012)   on 2011-08-07 19:27:13 (Show Source): You can put this solution on YOUR website! The situation is impossible. x + y odd ==> x, y must have different parities, i.e., x = odd and y = even, or x = even and y = odd. (If they have the same parity, then the answer is always even.) Now suppose x = odd and y = even. But , even though the quotient may be an integer (e.g., 90/15 = 6). Hence this situation is impossible. If x = even and y = odd, then , which will never produce an integer. Hence the situation is impossible.

Probability-and-statistics/478432: The council for aid to education reportes on the 2004 value of college and university endowments. Vanderbilt University ranked 21st. Find its pencentile in the top 150 colleges and universities. 1 solutions Answer 327820 by robertb(4012)   on 2011-08-06 05:44:02 (Show Source): You can put this solution on YOUR website! % = 86%, or 86th percentile.

Miscellaneous_Word_Problems/478468: Solve: x/x+1 + x+1/x=13/6 1 solutions Answer 327816 by robertb(4012)   on 2011-08-06 05:08:23 (Show Source): You can put this solution on YOUR website! ==> ==> ==> ==> 0 = (x +3)(x - 2) ==> x = -3,2. Both satisfy the original equation. These are the final answers.

Probability-and-statistics/478431: A student scored at the 98th percentile on a verbal test given to 1545 students. How many scored higher? 1 solutions Answer 327815 by robertb(4012)   on 2011-08-06 04:52:42 (Show Source): You can put this solution on YOUR website! 0.02*1545 = 30.9, and rounding down, 30 students scored higher.

Rate-of-work-word-problems/478463: If 4 men with 9 boys can do a piece of work in 6/5 days, and 3 men with 6 boys can do the same work in 12/7 days, how long would 1 boy alone take to do the work? 1 solutions Answer 327814 by robertb(4012)   on 2011-08-06 04:40:45 (Show Source): You can put this solution on YOUR website! Let 1/b = part of the work done by one boy in one day, and let 1/m = part of the work done by one man in one day. Then , and . ==> and ==> from the 2nd equation. ==> ==> ==> ==> ==> 1/18 of the work is done per boy per day. ==> It will take 18 days for one boy to finish the work.