shankar.ashwin wrote:WHat is the sum of the digits of (10^25) - 361?
A) 207
B) 216
C) 225
D) 234
E) 241
Start with an easier example:
10^4 - 361 = 10,000-361 = 9639.
Notice that 10^4 is a 5-digit integer -- the smallest possible.
When we subtract 361, the result is a 4-digit integer whose 3 rightmost digits are 6, 3, and 9. The remaining digit is 9.
10^25 is a 26-digit integer -- the smallest possible.
Thus, when we subtract 361, the result will be a 25-digit integer whose 3 rightmost digits are 6, 3, and 9. The remaining 22 digits will each be 9.
Sum = (22*9) + (6+3+9) = 216.
The correct answer is
B.
Last edited by
GMATGuruNY on Wed Sep 28, 2011 6:56 am, edited 2 times in total.
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