Cambridge Review TestPrep CD question

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wagoboy: Newbie | Next Rank: 10 Posts; Posts: 8; Joined: Wed Feb 13, 2008 8:23 am

by wagoboy » Wed Feb 13, 2008 8:27 am

If x^5 = 4, and x^4 = 5/y, what is y?

Sorry I can't recall the 5 choices, but would be great if someone can show how to break down this question

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Source: Beat The GMAT — Problem Solving | Wed Feb 13, 2008 8:27 am

torontogmat.com: Junior | Next Rank: 30 Posts; Posts: 26; Joined: Mon Feb 11, 2008 11:34 am; Location: Toronto; Thanked: 7 times

by torontogmat.com » Wed Feb 13, 2008 9:54 am

depends on whether the answer choices are numeric, or in terms of x.

you can ballpark a number in your head, but I'm assuming the answer choices will be in terms of x.

x = 4^(1/5) from statement 1.

therefore, x^4 = 4^(4/5) = 5/y, so y = 5 / 4^(4/5), which I'm guessing is just under 2.

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its_me07: Senior | Next Rank: 100 Posts; Posts: 83; Joined: Mon Oct 22, 2007 4:44 am; Thanked: 1 times

by its_me07 » Wed Feb 13, 2008 10:28 am

x^4.x=4
5x/y.x=4 as x^4=5/y
so
y=5x/4

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