Which of the following rational numbers is Not a perfect cube?

A. 827

B. 12564

C. - 64

D. 136

Answer: Choice D

We have 8/27 which can be written as (2/3) ^3, so 8/27 is a perfect cube.

Similarly, 125/64 = (5/4) ^3, showing that it too is a perfect cube. So far we have eliminated choices A and B.

Choice C is also eliminated because - 64 = (-4) ^3

Lastly, choice D is not a perfect cube assuming it is 136 because 136^ (1/3) = 5.142563 is not rational (ie not a fraction of whole numbers). The same can be said about 1/36 and 13/6 as well.