bigdady wrote:
A positive integer is divisible by 9 if and only if the sum of its digits is divisible by 9. If n is a positive integer, for which of the following values of k is \(25*10^n + k*10^{2n}\) divisible by 9?
(A) 9
(B) 16
(C) 23
(D) 35
(E) 47
is this from official source.
this is hard. many person do it wrongly
because k*10^2n has at least 1 number more than 25*10^n, we know that the sume of the two number will be
K25*10^x
for exam ple if k=52
the sume will be
5225*10^n
ONLY THIS CASE HAPPEN, we can add the digit, and find the answer is E.