Which fraction has a terminating decimal as its decimal expansion?

1. one third

2. one fifth

3. one seventh

4. one ninth

'One third' as a decimal is 1 : 3 = 0.333333 ... ⇒ The decimal is recurring

'One fifth' as decimal is 1 : 5 = 0.2 ⇒ The decimal terminates at the tenth value

'One seventh' as decimal 1 : 7 = 0.142857142857 ... ⇒ The decimal is recurring for every digit between 1 and 7

'One ninth' as decimal 1 : 9 = 0.111111 ... ⇒ The decimal is recurring

Answer: one fifth