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# Recent problems solved by 'robertb'

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 Age_Word_Problems/364810: John is now 3 times as old as his brother Sam. In 5 years, John will be twice as old as Sam will be then. What are their present ages?1 solutions Answer 260081 by robertb(4012)   on 2010-11-01 20:10:13 (Show Source): You can put this solution on YOUR website!j = 3s, j+5 = 2(s+5). By direct substitution, 3s+5 = 2s+10, 3s-2s = 10-5, s = 5, the age of sam, while, j = 3*5 = 15, the age of john.
 Square-cubic-other-roots/364741: can you show me step by step on how to rationalize the denominator for this expression. cube root of (2x/9y)1 solutions Answer 260078 by robertb(4012)   on 2010-11-01 20:06:13 (Show Source):
 Rectangles/364740: The length is five units more than the width. The permeter is 9 times thw width. what is length and width?1 solutions Answer 260071 by robertb(4012)   on 2010-11-01 19:57:51 (Show Source): You can put this solution on YOUR website!l = w+5, Perimeter is 2l+2w, and so 2l+2w = 9w. By direct substitution, 2(w+5)+2w = 9w. 2w+10+2w = 9w, 4w+10 = 9w, 10 = 5w, w = 2, the width, while the length is 7.
 Angles/364739: The measure of the supplement of an angle is 30 more than four times the measure of the complement of the angle. Find the measure of the complement1 solutions Answer 260069 by robertb(4012)   on 2010-11-01 19:53:51 (Show Source): You can put this solution on YOUR website!Let x = angle. Then 180 - x = 4(90-x)+30, 180- x = 360-4x+30, 180-x = 390-4x, 4x-x = = 390 - 180, 3x = 210, x = 70, measure of the unknown angle. Thus, the complement is 20.
 Surface-area/364745: what is the greatest possible area of a rhombus constructed on an 11-by-14 inch sheet of paper?1 solutions Answer 260055 by robertb(4012)   on 2010-11-01 18:29:24 (Show Source): You can put this solution on YOUR website!The greatest possible area is sq.inches.
 Equations/364721: x+5=2x+31 solutions Answer 260054 by robertb(4012)   on 2010-11-01 18:27:26 (Show Source): You can put this solution on YOUR website!x+5 = 2x+3, 5-3 = 2x-x, 2 = x, or x = 2.
 Polynomials-and-rational-expressions/364722: Find the LCM: 14b^6 a^8, 7b^7 a^8, 10b^2 a^31 solutions Answer 260053 by robertb(4012)   on 2010-11-01 18:26:30 (Show Source): You can put this solution on YOUR website!LCM is
 Surface-area/364727: Find the volume of a cylinder whose height is 2 m and whose base has an area of 9πm 2nd1 solutions Answer 260052 by robertb(4012)   on 2010-11-01 18:24:48 (Show Source): You can put this solution on YOUR website!sq.m.
 Functions/364734: Round all answers to the nearest cent. At 2:00pm Braden rented a mountain bike at 5:00, after cycling 18 miles Braden paid \$12 for the rental. A) Find Braden's average speed, in miles per hour. B) Find the rental rate, in dollars per hour. C)Find the rental rate, in dollars per mile. Thank you1 solutions Answer 260051 by robertb(4012)   on 2010-11-01 18:22:58 (Show Source): You can put this solution on YOUR website!A) 18 miles/3 hours = 6mi/hr. B)\$12/3 hours = \$4/hr. C)\$12/18 miles = \$0.67/mi.
 Expressions-with-variables/364737: a=a+b+c/3 for c 1 solutions Answer 260050 by robertb(4012)   on 2010-11-01 18:19:35 (Show Source): You can put this solution on YOUR website!, , , .
 Expressions-with-variables/364736: How do I solve -5x-10=2-(x+4) I really don't understand how to figure it out I've 5 different times and still can't get it.1 solutions Answer 260049 by robertb(4012)   on 2010-11-01 18:17:27 (Show Source): You can put this solution on YOUR website!-5x-10 = 2-(x+4), -5x-10 = 2-x-4, -5x-10 = -x-2, -5x + x = -2+10, -4x = 8, x = -2.
 Quadratic_Equations/364733: factor each trionimal,if possible. 3a2+13a+4 1 solutions Answer 260048 by robertb(4012)   on 2010-11-01 18:15:19 (Show Source):
 Probability-and-statistics/364731: From what I read, I stated that it was true. I just wanted to make sure I am understanding what I read. The standard error of the mean is the standard deviation of the population from which the samples have been taken. T-F, and why or why not? 1 solutions Answer 260047 by robertb(4012)   on 2010-11-01 18:14:09 (Show Source): You can put this solution on YOUR website!False. The standard error of the mean is the standard deviation of the population from which the samples have been taken DIVIDED BY the square root of the sample size.
 Probability-and-statistics/364405: Suppose that the average number of students to ride the elevator is 2.4 persons per 10 minutes during the week (does not matter what time, nor the day). What is the probability that less than 4 students ride the interval today from 11:00 – 11:10? 1 solutions Answer 259827 by robertb(4012)   on 2010-11-01 02:24:05 (Show Source): You can put this solution on YOUR website!This is a poisson experiment with . Then . Hence the probability is
 Probability-and-statistics/364399: A foreman at a large plant estimates defective parts about 1% of the time. If the plant produces 30,000 parts in a week, what is the standard deviation (to the nearest tenth) for the number of defective parts?1 solutions Answer 259826 by robertb(4012)   on 2010-11-01 02:10:17 (Show Source): You can put this solution on YOUR website!This is a binomial experiment with n = 30000, p = 0.01, and q = 1-p = 0.99. The mean is and the standard deviation is , to 4 decimal places.
 Travel_Word_Problems/364391: The jones family drove to disneyland at 5 miles per hour and returned on the same route at 4 miles per hour. Find the distance to disneyland if the total driving time was 7.2 hours.1 solutions Answer 259805 by robertb(4012)   on 2010-10-31 23:45:53 (Show Source): You can put this solution on YOUR website!, , , d = 16 miles.
 Probability-and-statistics/364371: 3. The amount of time (in minutes) devoted to commercials on a TV channel during any half-hour program is normally distributed with a mean of 6.3 minutes and a standard deviation of 0.866 minutes. What is the probability that a person who watches 20 half-hour programs will see less than 2 hours of commercials?1 solutions Answer 259804 by robertb(4012)   on 2010-10-31 23:42:36 (Show Source): You can put this solution on YOUR website!Let X = random variable representing the amount of time (in minutes) devoted to commercials on a TV channel during any half-hour program. Then , and . Then Y = 20X is the r.v. representing the amount of time (in minutes) devoted to commercials on a TV channel during 20 half-hour programs. This r.v. is also normally distributed with mean 0.63*20 = 126 minutes, and SD = 20*0.866 = 17.32 minutes. Then P(Y<120) = P(Z< -0.346) = 0.365, approximately.
 Mixture_Word_Problems/364370: Mia needs to make 10 liters of a solution that is 10% salt. Solution A is 5% salt and Solution B is 25% salt. Which system of equations can Mia use to find the number of liters of each solution she should combine? (Let x be the number of liters of Solution A, and y be the number of liters of Solution B.) 1 solutions Answer 259794 by robertb(4012)   on 2010-10-31 23:14:34 (Show Source): You can put this solution on YOUR website!0.05x + 0.25(10-x) = 0.10*10, 0.05x + 2.5 - 0.25x = 1, -0.2x = -1.5, x = 7.5, # liters of 5% salt solution, 2.5 liters of 25% solution.
 Systems-of-equations/364384: what is the value of the discriminant 20x^2 + 5x + 191 solutions Answer 259791 by robertb(4012)   on 2010-10-31 23:06:18 (Show Source):
 Polynomials-and-rational-expressions/364381: Find all of the real solutions of the polynomial equation. x^5 - x^4 -3x^3 + 5x^2 -2x = 0 So far I have gotten that I would need to take out an x x(x^4 - x^3 -3x^2 +5x -2)1 solutions Answer 259789 by robertb(4012)   on 2010-10-31 23:04:12 (Show Source): You can put this solution on YOUR website!Factoring out x would give . Now , so that the polynomial equation is. The roots are 0, -2, or 1 (multiplicity 3).
 Linear-equations/364380: Find the missing coordinate. A=(3,2)and B= (7,__) m = -21 solutions Answer 259787 by robertb(4012)   on 2010-10-31 22:58:41 (Show Source): You can put this solution on YOUR website! from the slope formula. , , . The missing coordinate is -6.
 Rational-functions/364382: Find the lcm of (6+7w), (36-49w^2),and (6-7w)?1 solutions Answer 259784 by robertb(4012)   on 2010-10-31 22:55:25 (Show Source): You can put this solution on YOUR website!is the lcm.
 Probability-and-statistics/364104: We believe that 90% of the population of all Calculus I students consider calculus an exciting subject. Suppose we randomly and independently selected 21 students from the population. If the true percentage is really 90%, find the probability of observing 20 or more of the students who consider calculus to be an exciting subject in our sample of 21.1 solutions Answer 259780 by robertb(4012)   on 2010-10-31 22:43:08 (Show Source): You can put this solution on YOUR website!0.90 = probability that a student finds calculus exciting. THEN...0.10 = probability that a student finds calculus not exciting. This is a binomial experiment with p = 0.90 and n = 21. Therefore the probability of observing 20 or more of the students who consider calculus to be an exciting subject in our sample of 21 is given by: , to 5 decimal places.
 absolute-value/96935: /2x-1/ greater than or equal to 01 solutions Answer 259670 by robertb(4012)   on 2010-10-31 04:39:20 (Show Source): You can put this solution on YOUR website!By definition any absolute-value is non-negative, and thus there is no need for solving here: any real value of x is a solution of the inequality.
 Radicals/363976: 1.explain why 3[sqrt] x^6=x2 for any value of x, but x[sqrt^6]= x3 only when x ≥ 0. 1 solutions Answer 259669 by robertb(4012)   on 2010-10-31 04:31:52 (Show Source): You can put this solution on YOUR website!The cube root of is equal to for any value of x because the sign of x is retained by the presence of the power 2. But can take on only non-negative values (because it is a square root!). Technically speaking, = ||, and so there would be a problem if x<0. For example, if we allow x <0, then , but a square root is always non-negative!
 Polynomials-and-rational-expressions/363936: x3 + 3x2 + -8x + -24 factor by grouping 1 solutions Answer 259668 by robertb(4012)   on 2010-10-31 04:13:42 (Show Source):
 Probability-and-statistics/363925: 1.A die is rolled and a card is selected from a standard 52 card deck. What is the probability of rolling a 3 and selecting a red card? 2. Jim rolls two dice. Let the sum of the dice be the value of the first die added to the value of the second die. Find the probability of Jim rolling a sum greater than 8. 3. Two cards are drawn from a standart deck of 52 cards without replacement. Find the probability that both cards drawn are: Aces, Red Aces. 4. If four fair dice are rolled, what is the probability that each of the four numbers that appear will be different? 1 solutions Answer 259667 by robertb(4012)   on 2010-10-31 04:10:37 (Show Source): You can put this solution on YOUR website!1.A die is rolled and a card is selected from a standard 52 card deck. What is the probability of rolling a 3 and selecting a red card? I'm assuming that you are rolling a fair 6-sided die. Then the prob'y . 2. Jim rolls two dice. Let the sum of the dice be the value of the first die added to the value of the second die. Find the probability of Jim rolling a sum greater than 8. There are 4 possibilities for a sum of 9, 3 for 10, 2 for 11, and 1 for 12. Thus the probability is 10/36, or 5/18. 3. Two cards are drawn from a standard deck of 52 cards without replacement. Find the probability that both cards drawn are: Aces, Red Aces. For aces, probability is . For both red aces, probability is . 4. If four fair dice are rolled, what is the probability that each of the four numbers that appear will be different? Probability is .
 Human-and-algebraic-language/364033: Translate the following situation into an inequality. Do not solve. "The sum of three integers is no more than 110. If one integer is nine less than twice the first integer and the third integer is one fourth the first integer, what are the ingegers?" 1 solutions Answer 259666 by robertb(4012)   on 2010-10-31 03:45:17 (Show Source): You can put this solution on YOUR website!"The sum of three integers is no more than 110. If one integer is nine less than twice the first integer and the third integer is one fourth the first integer, what are the integers?" . Also , and .
 Rational-functions/364032: find the axis of the graph of the function F(X)=(X+9)^2 - 1 1 solutions Answer 259665 by robertb(4012)   on 2010-10-31 03:40:07 (Show Source): You can put this solution on YOUR website!. This is vertex-form equation of a parabola with vertex at (-9, -1) with axis of symmetry parallel to the y-axis. Thus the axis of symmetry is x = -9.
 Probability-and-statistics/364055: In favor Not in favor Not sure Northeast: In favor_68%; Not in favor_29%; Not sure_3% Midwest: In favor_69%; Not in favor_29%; Not sure_2% South: In favor_72%; Not in favor_23%; Not sure_5% West: In favor_80%; Not in favor_19%; Not sure_1% a. if three adults are selected at random from Northeast, what is the probability that all are in favor of the death penalty? 1 solutions Answer 259664 by robertb(4012)   on 2010-10-31 03:34:28 (Show Source): You can put this solution on YOUR website!. Hope that helps.
 Probability-and-statistics/364056: Northeast: In favor_68%; Not in favor_29%; Not sure_3% Midwest: In favor_69%; Not in favor_29%; Not sure_2% South: In favor_72%; Not in favor_23%; Not sure_5% West: In favor_80%; Not in favor_19%; Not sure_1% a/ If three adults are selected at random from Northeast, what is the probability that all three are in favor of the death penalty? Please, explain in details thank you1 solutions Answer 259663 by robertb(4012)   on 2010-10-31 03:32:59 (Show Source): You can put this solution on YOUR website!. Hope that helps.