Problem solving

[Noman]

plz explain
if y=4^10+4^11+4^12+4^13, then y is the divisible by which number?
A.12 B.13 C.17 D.19 E.23

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Hi Noman,

We're told that Y = 4^10 + 4^11 + 4^12 + 4^13

We can 'factor out' 4^10 from each of those 'pieces', which gives us...

4^10 + 4^11 + 4^12 + 4^13 =
4^10 (4^0 + 4^1 + 4^2 + 4^3) =
4^10 (1 + 4 + 16 + 64) =
4^10 (85) =
4^10 (5)(17) =

We're asked which of the 5 answers is divisible into Y.

Final Answer: C

GMAT assassins aren't born, they're made,
Rich