Which fraction is in reduced form?

A 4/20 B 6/9 C 5/13 D 14/21

C 5/13

Step-by-step explanation:

A fraction is written in reduced form if there are no common factors in the numerator and denominator. Since you know your multiplication tables, you can easily identify the common factors:

A 20 = 5·4, so 4 is a common factor 4 / (4·5) = 1/5

B 6 = 2·3, 9 = 3·3, so 3 is a common factor (2·3) / (3·3) = 2/3

C 13 is not a multiple of the prime number 5, so there are no common factors. 5/13 is a reduced fraction

D 14 = 2·7, 21 = 3·7, so 7 is a common factor (2·7) / (3·7) = 2/3