SAT 2013

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Question: 
Permutations and Combinations

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Asked by Astha

The test on Permutations and Combinations kind of went over my head! Can anybody explain it to me!!!


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    oLahav
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    Oren LahavTue, 22 Jul 2008 13:29:36 -0000

    You will not need any permutation or combination knowledge (other than super basic stuff you can find here ) for the SAT.

    I can help with a few of the questions on that test if you just want to know the answers:

    For question 1, the number of diagonals in a polygon with n sides is given by D=n(n-3)/2, and you just plug in D=11 and solve for n. You can also figure it out without a formula, going by number of sides from 7 up and just drawing polygons and counting diagonals, but it'll take long.

    For question 2, you have 10 digits to select, and each digit has 2 choices- 3 or 7. Since it's an "and" scenario for all of the digits, you multiply them- you'll get 2 ^ 10.

    For question 4- the formula for handshakes would be H=n(n-1)/2 for n people, since each person shakes hands with everybody by himself n(n-1), but if Harry shakes John it's the same as John shakes Harry, so you divide by 2. Then solve for n same as question 1.

    For question 5- draw the lines diagonally, it's a bit confusing but you can eventually see it.

    Question 3 there's a trick which I can't think of yet, I'm still working on it.

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    astha shuklaWed, 23 Jul 2008 05:53:30 -0000

    Thanks I did refer to a few books and seriously the test is tougher than SAT level.

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    oLahav
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    Oren LahavWed, 23 Jul 2008 13:41:25 -0000

    I agree. The test is probably more towards GMAT level preparation, which is why it's in that community too.

    However, I find that these type of short, challenging tests are fun from time to time. Don't worry if you can't figure it all out though, the SAT doesn't contain permutations or combinations, and even if it did you wouldn't need any background theory to handle them, they would be perfectly solveable using basic logic.

    Good luck.

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