一道难题，求教大家

alanzr

Q15:
Which of the following fractions has a decimal equivalent thatis a terminating decimal?
A. 10/189
B. 15/196
C. 16/225
D. 25/144
E. 39/128
答案是E, 请问大家什么思路？

chinamerica

Terminating decimals represent a rational number in the form  k/(2^n5^m), i.e., the denominator cannot have any prime factor other than 2 and 5.
Notice that 128= 2^6.
The denominators in the other terms have prime factor(s) other than 2 and 5.

alanzr

除了2和5，其他的， 如11,13,17 都不行吗？，这个规律是做题的经验总结，还是可以证明的规律？