prep question

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prep question

by dunkin77 » Tue Apr 24, 2007 12:55 pm
Hi,

I thought I was correct but the answer was 15. Can you please help?
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by Neo2000 » Tue Apr 24, 2007 5:49 pm
Always think about checking your work by substituting the answer you got back into the question

In any case
taking 2^(X-2) common you get

2^(X-2)[2^2 -1] = 3(2^13)
2^(X-2)[3] = 3(2^13)


Thus you can see that 2^(X-2)=(2^13)

OR X-2 = 13
X = 15

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by Cybermusings » Wed Apr 25, 2007 4:48 am
2^x - 2^(x-2) = 3 (2^13)
Take 2^(x-2) common here

2^(x-2)*[2^2 - 1] = 3(2^13)
2^(x-2)*[4-1]= 3(2^13)
2^(x-2)*[3]= 3(2^13)
2^(x-2)=2^13
Or x-2=13
Thus x = 15(base of the two powers are the same so equate the powers)