Math Question

[MATH MATH MATH]

Hi All,

If 4^4x = 1600, what is the value of (4x-1)2?

So, the first hing I did (which may be totally wrong) is divide each side by 4. Leaving me with 4X = 1600. This could not have been farther from the right answer. Could someone please explain the rule of why I can't do this? In some other problems I have seen people multiply and divide with an exponent...so why can't I do it here?

Thanks so much!!

[Guest]

Are you sure you typed this problem correctly? As written, x~1.33, but I have no idea how you would determine this without using numerical methods that either require a calculator or a lot more time than you have on the GMAT.

[Guest]

Can you provide the answer choices? If it's enough to see that x is between 1.25 and 1.375, then I see how you could solve this, otherwise I have no idea:

4^4x=1600

2^8x=1600
2^8x=64*25
2^8x=2^6*25
2^(8x-6)=25

Given that 2^4 = 16 and 2^5 =32 we have

(8x-6) > 4 and (8x-6)<5

which gives

1.25<x<1.375

[RonPurewal]

Please post the SOURCE of all questions that you present on this forum, including name of collection and problem # (if applicable). If you don't, then we'll have to remove the problem from the forum.

thanks.