Find the number halfway between 3/5 and 7/10

The answer is 13/20

The number (n) halfway between x and y is:

n = (x + y) : 2

The number (n) halfway between 3/5 and 7/10 is:

n = (3/5 + 7/10) : 2

n = (6/10 + 7/10) : 2

n = 13/10 : 2

n = 13/10 : 2/1

n = 13/10 * 1/2

n = 13/20