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Chriszzz

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  • Location
    Atlanta gA
  • Application Season
    2013 Spring
  • Program
    CS

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  1. Hi guys, first time poster here. I ran into some confusion while using Sid Thatte's GRE/GMAT math book. There are two probability practice problems which Mr. Thatte seems to solve with different approaches. They are as follows: Question 1 (dice-sum problem). If you roll two dice, what's the probability that the sum of the two numbers you get will be 6? Question 2 (list-product problem). If you have two lists of numbers, list A being 1-3-5 and list B being 2-5-6, you select one number from each list, what is the probability that the product of the two numbers will be odd? My confusion is in the way the book calculates the denominator (aka the total # of outcomes) of each probability. In the dice-sum problem, they counted the total # of outcomes as the number of dice roll arrangements, not as the total # of unique sums. In the list-product problem, they did the exact opposite and counted the total # of outcomes as the number of unique products that were possible, not the total # of arrangements of number choices. i.e., in the dice-sum problem, the book counts 36 total possible outcomes, which is 6*6, or the number of total arrangements/permutations of the two dice rolls. They did not use the total # of sums possible, which would be 11. In the list-product problem, the book counts 8 total possible outcomes from the 8 possible products between the numbers within the two lists (2,5,15,1,10,25,30). They did not use the total # of numerical arrangements, which would be 17 (3*3*2, minus one because picking 5, then another 5 is the same thing as its reverse) My question is, is this an error in the book or are the different approaches because of the different nature of the two problems (dice roll vs pick-a-number)? And if these were official ETS questions, how would I be expected to answer? Thanks
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