A Number Divided by 3D

A number when divided by D leaves a remainder of 8 and when divided by 3D leaves a remainder of 21 . What is the remainder left, when twice the number is divided by 3D?

a) 13 b) cannot be determined c) 3 d) 42

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MBA

Aug 11th, 2011

suppose the no. is a
a = Dx +8 ...1
a = 3Dy + 21 ...2
So from 1 & 2 we get
D(x-3y) = 13
13 is prime so x-3y has to be 1
let x = 4 and y = 1
We get a = 60
2a = 120
So 120 when divided by 3D = 39
we get remainder as 3
So answer is 3