If 4^k = m

[Brent@GMATPrepNow]

If 4^k = m, then 16^(4k+1) =
A) 4m^16
B) 8m^16
C) 16m^4
D) 16m^8
E) 256m^4

Please note that this is not an official GMAT question; it’s my attempt to create difficult (650+ level) GMAT-style questions for this forum.

[sacx]

16^(4k+1) = 4^2(4k+1)
= 4^(8k+2)
= (4^8k)(4^2)
=[(4^k)^8] (4^2)
=[m^8](16) (from 4^k = m)
= 16(m^8)

[Brent@GMATPrepNow]

Nice work - D it is