sivaelectric wrote:If 2^X - 2^(X-2) = 3 x 2^17, What is the value of X?
A. 16
B. 17
C. 18
D. 19
E. 20
We can plug in the answers, which represent the value of X.
Answer choice C: 18.
2^18 - 2^(18-2) = 3 * 2^17
2^18 - 2^16 = 3 * 2^17
2*16(2^2 - 1) = 3 * 2^17
2^16 * 3 = 3 * 2^17.
Doesn't work. Eliminate C.
To match 2^17 on the right side of the equation, the exponent on the left side of the equation needs to be increased by 1.
The correct answer is
D.
Answer choice D: 19.
2^19 - 2^(19-2) = 3 * 2^17
2^19 - 2^17 = 3 * 2^17
2*17(2^2 - 1) = 3 * 2^17
2^17 * 3 = 3 * 2^17.
Last edited by
GMATGuruNY on Mon Jun 06, 2011 7:46 am, edited 1 time in total.
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