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# Recent problems solved by 'robertb'

robertb answered: 4011 problems
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 Travel_Word_Problems/390906: The distance from a star to a planet is 9.1 X 10^18 m. How long does it take light, traveling at 10^16 m/year, to travel from the star to the planet?1 solutions Answer 277259 by robertb(4012)   on 2011-01-05 05:04:23 (Show Source): You can put this solution on YOUR website! years, or 910 years.
 Functions/390884: find the domain and range of each relation . [(-3, -7),(-1, -3),(0,-1),(2,3),(4,7)]1 solutions Answer 277258 by robertb(4012)   on 2011-01-05 05:01:08 (Show Source): You can put this solution on YOUR website!Domain = {-3, -1, 0, 2, 4} Range = {-7, -3, -1, 3,7}
 Inverses/390918: 1/1.4+1/4.7+1/7.10+1/10.13+1/13.16=?1 solutions Answer 277257 by robertb(4012)   on 2011-01-05 04:57:53 (Show Source): You can put this solution on YOUR website!5/16
 Miscellaneous_Word_Problems/390919: Express the area A of a square in terms of its perimeter p1 solutions Answer 277255 by robertb(4012)   on 2011-01-05 04:56:10 (Show Source):
 Inverses/390917: 1/1.4+1/4.7+1/7.10+1/10.13+1/13.161 solutions Answer 277253 by robertb(4012)   on 2011-01-05 04:54:25 (Show Source): You can put this solution on YOUR website! = = .
 Inverses/390915: 1/2+1/6+1/12+1/20+1/30...1/n(n+1)1 solutions Answer 277252 by robertb(4012)   on 2011-01-05 04:40:24 (Show Source): You can put this solution on YOUR website!+...+ =+...+ = because of "telescoping" property.
 Trigonometry-basics/389458: A box has the dimensions of 2 inches by 3 inches by 4 inches. Determine the approximate angle formed by the diagonal of the 2 X 3 side and the diagonal of the 3 X 4 side to the nearest degree?1 solutions Answer 277251 by robertb(4012)   on 2011-01-05 04:33:35 (Show Source): You can put this solution on YOUR website!Let the length of the base be 4 inches, the width of the base be 3 inches, and the height, 2 inches. Then the measure of the diagonal of the 2x 3 face is , the measure of the diagonal of the 3x 4 face is 5, and the measure of the diagonal of the 2x 4 face is . The three diagonals form a triangle. Then from the cosine law, ===> ===> ===> degrees, to the nearest degree.
 test/390913: if 5/7 of a number is 35.what is the number? 1 solutions Answer 277249 by robertb(4012)   on 2011-01-05 04:03:13 (Show Source): You can put this solution on YOUR website!Since , the number is 49.
 Travel_Word_Problems/390874: A car goes at v mph for a hours then goes in the opposite direction at u mph for b hours. How far is the car from where it started at the end?1 solutions Answer 277248 by robertb(4012)   on 2011-01-05 04:00:55 (Show Source): You can put this solution on YOUR website!|u*b - v*a| miles.
 Travel_Word_Problems/390886: Two jets are traveling toward each other and are 4000 km apart. The rate of one jet is 100 km/h faster than the rate of the other. If the jets pass each other after 2.5 hours, what is the rate of the faster jet?1 solutions Answer 277247 by robertb(4012)   on 2011-01-05 03:56:44 (Show Source): You can put this solution on YOUR website!2.5x + 2.5(x+ 100) = 4000 ===> 2.5x + 2.5x +250 = 4000 ===> 5x = 3750 ===> x = 750 kph, the rate of one jet, x + 100 = 850 kph, the rate of the faster jet.
 Linear-equations/390911: If f(x) = 2x - 3, evaluate the following: ( a ) f(-2) = ( b ) f(t) ( c ) f(a - 2) 1 solutions Answer 277246 by robertb(4012)   on 2011-01-05 03:47:06 (Show Source): You can put this solution on YOUR website!f(-2) = 2*-2 - 3 = -4-3 = -7. f(t) = 2t - 3. f(a-2) = 2*(a-2) - 3 = 2a - 4 - 3 = 2a - 7.
 Proportions/390893: Jeremy bought a souvenir while on vacation. The item cost \$22.00, but the otal bill was \$23.43, What percent was the sales tax? Use a percent equation and Use a proportion1 solutions Answer 277245 by robertb(4012)   on 2011-01-05 03:45:20 (Show Source): You can put this solution on YOUR website!% sales tax.
 Percentage-and-ratio-word-problems/390895: Wayne has milk that is 5% butterfat and skim milk without butterfat. How much 5% milk and how much skim milk should he mix to make 200 gallons of milk that is 3.5% butterfat?1 solutions Answer 277244 by robertb(4012)   on 2011-01-05 03:40:56 (Show Source): You can put this solution on YOUR website!0.05x + 0.00*(200 - x) = 0.035*200 ===> 0.05x = 7 ===> x = 140 gallons of the 5% milk, and 60 gallons of the skim milk.
 Proportions/390892: "If the 481 children's books represent 13% of the books in the library, how many total books are in the library?" Use a percent equation and Use a proportion 1 solutions Answer 277243 by robertb(4012)   on 2011-01-05 03:32:02 (Show Source): You can put this solution on YOUR website!0.13x = 481 ===> x = 481/0.13 = 3700 books.
 Probability-and-statistics/390910: in a cellular phone area, company A accounts for 70% of the cellular phone market, while company B accounts for the remaining 30% of the market. Of the cellular calls made with company A, 2% of the calls will have some sort of interference, while 3% of the cellular calls with company B will have interference. if a cellalar call is selected at , the probability that it will not have interference is........1 solutions Answer 277242 by robertb(4012)   on 2011-01-05 03:30:05 (Show Source): You can put this solution on YOUR website!0.7*0.98 + 0.3*0.97 = 0.977
 Percentage-and-ratio-word-problems/390889: A pharmacist needs 500 milliliters of a 10% phenorbarbital solution. She only has 5% and 25% solutions available. How many milliliters of each solution should she mix to obtain the desired solution? 1 solutions Answer 277241 by robertb(4012)   on 2011-01-05 03:24:18 (Show Source): You can put this solution on YOUR website!0.05*x + 0.25*(500 - x) = 0.10*500; 0.05x + 125 - 0.25x = 50; -0.20x = -75; x = 375 milliliters of the 5% solution, and 500 - x = 125 milliliters of the 25% solution.
 Trigonometry-basics/390905: Hello, Please hep me to solve this problem: Find all exact value solutions [o,360) for sin^2x-2sinx-3 = 0 My work: x^2-2x-3 = 0 sinx = 3 sinx = -1 sin^-1(3) = None sin^-1(-1) = -90 1 solutions Answer 277239 by robertb(4012)   on 2011-01-05 02:47:07 (Show Source): You can put this solution on YOUR website!sin^-1(-1) = -90 is actually correct, BUT -90 is not in [0, 360), so the desired solution is -90 + 360 = 270.
 test/390908: The differences between primitive root and primitive element of a finite field. And also the difference between primitive element and generator of a finite field.1 solutions Answer 277238 by robertb(4012)   on 2011-01-05 02:42:21 (Show Source): You can put this solution on YOUR website!Hmm. Look at http://en.wikipedia.org/wiki/Primitive_element_%28finite_field%29. You must be a math major in 2nd, 3rd year college? Or a college math professor? Ha ha. There are some excellent books in abstract algebra/Galois theory you can look at, like Gallian, Fraleigh, Hungerford, Artin, to name a few.
 Proportions/390900: if a,b,c are in continued proportion, prove that: (a^2+b^2+c^3)/(a+b+c)=a-b+c and hence find three numbers in continued proportion so that their sum is 14 and the sum of their squares is 84 1 solutions Answer 277237 by robertb(4012)   on 2011-01-05 02:37:18 (Show Source): You can put this solution on YOUR website!You definitely mean . The given is , that is, a,b,c are in continued proportion . One consequence of this condition is the fact that , which we will use later. To start off, consider . Upon expansion, this is equal to . But , so after substitution, . Assuming that the sum a+b+c is not equal to zero, then we divide by a+b+c, and the result follows. Consider a = 8, b = 4, and c = 2. Then .
 Evaluation_Word_Problems/390610: A biology class did a survey of an open field for the number of visible insects per square ft. of ground. The results were normally distributed. The mean was 28 insects and the standard deviation was 5. What values are 1 standard deviation from the mean?1 solutions Answer 277231 by robertb(4012)   on 2011-01-04 22:58:07 (Show Source): You can put this solution on YOUR website!Use the z-score formula: . Hence we want +/-, or +/-5 = X - 28, or X = 23, 33.
 Travel_Word_Problems/390875: Express the area A of a square in terms of its perimeter p.1 solutions Answer 277228 by robertb(4012)   on 2011-01-04 22:51:21 (Show Source):
 Mixture_Word_Problems/390739: How many milliliters of water must be added to 60 mL of a 15% iodine solution in order to dilute it to a 10% iodine solutioN?1 solutions Answer 277225 by robertb(4012)   on 2011-01-04 22:41:32 (Show Source): You can put this solution on YOUR website!60*0.15 + x*0.00 = (60 + x)*0.10; 9 = 6 + 0.10x; 3 = 0.10x; x = 30 mL of water must be added.
 Travel_Word_Problems/390873: A car travels y miles in t hours, what is its speed? 1 solutions Answer 277224 by robertb(4012)   on 2011-01-04 22:39:03 (Show Source): You can put this solution on YOUR website!y/t miles per hour AVERAGE speed.
 Travel_Word_Problems/390734: one car travels west at 72 mph and another car travels north at 21 mph whats their distance after an hour1 solutions Answer 277223 by robertb(4012)   on 2011-01-04 22:36:59 (Show Source): You can put this solution on YOUR website!The distance is miles apart.
 Percentage-and-ratio-word-problems/390740: If 50 million people traveled for 2010 and only 14 million traveled by air; what percentage traveled by air?1 solutions Answer 277222 by robertb(4012)   on 2011-01-04 22:34:17 (Show Source): You can put this solution on YOUR website!(14/50)*100% = 28% traveled by air.
 Permutations/390858: Signals are made by running five colored flags up a mast. How many different signals can be made if there is an unlimited supply of flags of seven colors?1 solutions Answer 277218 by robertb(4012)   on 2011-01-04 22:31:11 (Show Source): You can put this solution on YOUR website! signals assuming repetition of colors.
 Travel_Word_Problems/390857: A car travels 140 miles in 2 hours at constant speed. What was the speed?1 solutions Answer 277216 by robertb(4012)   on 2011-01-04 22:28:35 (Show Source): You can put this solution on YOUR website!140/2 = 70 miles per hour.
 Travel_Word_Problems/390861: A car travels for t hours at 100 mph how far does it go? 1 solutions Answer 277215 by robertb(4012)   on 2011-01-04 22:27:50 (Show Source): You can put this solution on YOUR website!100t miles.
 Probability-and-statistics/390733: What proportion of the data is between the first and third quartiles?1 solutions Answer 277210 by robertb(4012)   on 2011-01-04 22:22:23 (Show Source): You can put this solution on YOUR website!The 1st quartile Q1 demarcates the lowest 25% of the distribution from the higher 75%. The 3rd quartile Q3 demarcates the lower 75% of the distribution from the highest 25%. (We are assuming here that the values of the RV are either in increasing or decreasing order.) What is in between the Q1 and Q3 then, is exactly 50% of the distribution. (Think of it this way: Exclude the lowest 25% of the distribution and the highest 25% of the distribution and you get exactly the middle 50% of the distribution.)
 test/390728: The quadratic parent function is translated 2 units left and 1 unit up. What is the new quadratic equation, in vertex form?1 solutions Answer 277203 by robertb(4012)   on 2011-01-04 22:10:40 (Show Source): You can put this solution on YOUR website!If the quadratic "parent" function is , then the "offspring" function is .
 Mixture_Word_Problems/390845: a juice bar mixes apple juice and cranberry juice. how much should you charge if you mix 8 l of apple juice selling 45 cents/liter with 10 l of cranberry juice for \$1.08/liter?1 solutions Answer 277199 by robertb(4012)   on 2011-01-04 22:06:12 (Show Source): You can put this solution on YOUR website!8*0.45 + 10*1.08 = 18*x; 14.4 = 18x; x = \$0.80 per liter.