是不是真的要算出来？

Xiaotongdi

Which of the following fractions has a decimal equivalent that is a terminating decimal?
A. 10/189  
B. 15/196
C. 16/225
D. 25/144
E. 39/128

这种题是不是真的要把他们给算出来？有没有快捷的？

sdcar2010

No.  

EEEEEEEEEEE since 128 only has 2 as its factors.

Xiaotongdi

什么叫只有2是因子？

clytzejjx

把分母分解质因数就好了

A. 3^3*7
B. 2^2*7^2
C. 5^2*3^2
D. 3^2*2^4
E. 2^7

肯定是选E咯。。。

pqylovelva

The answer is E.

For a fraction to be a terminating decimal the denominator can contain only the prime factors 2 and/or 5 i.e. the denominator should be in the form

Looking at each denominator.

A. 189 has the prime factor 3 so the fraction is not a terminating decimal.
B. 196 has the prime factor 7 so the fraction is not a terminating decimal.
C. 225 has the prime factor 3 so the fraction is not a terminating decimal.
D. 144 has the prime factor 3 so the fraction is not a terminating decimal.
E. 128 has the prime factor 2 only and can be written in the form  which makes the fraction a terminating decimal.

You can google that, I always do thatHere is the original link The answer is E.

http://gmatclub.com/forum/decimal-equivalent-80687.html

Xiaotongdi

ok! thank you so much!