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Re: What is the sum of the digits of integer x, where x = 4^10 x [#permalink]
05 Nov 2017, 06:23

We can rearrange the expression for x as \(2^7*(2*5)^{13}\) so that \((2*5)^{13}\) is equal to 1 followed by 13 zeros so that when it is multiplied by any number is equal to that number followed by 13 zeros. Then, \(2^7 = 128\) so that multiplied by the power of 10 becomes 128 and 13 zeros. Since we have to sum the digit of this number, we get 1+2+8+13*0 = 11.