All of the following are terminating decimals except
1/8
2/5
2/3
17/50

A terminating decimal is a decimal that has numbers that DO NOT go on forever. 
To figure this out we need to divide the fractions given:

1/8=0.125

2/5=0.4

2/3=0.666666666666=> (repeating) 

17/50=0.34

As you can see the only fraction that has a repeating decimal (and is not a terminating decimal is 2/3). Therefore our answer is 2/3 

First of all, what is a terminating decimal, a decimal that does keep repeating and going on forever. 1/8 = 0.125 CHECK! 2/5 = 0.4 CHECK! 2/3 = 0.666666666666666666666 BIG X! 17/50 = 0.34 CHECK! The only BIG X was 2/3 and 2/3 is our answer.