Verified answer

1/5 = (1·3)/(5·3) = 3/15 - доп. множ. 3

4/15 + 1/5 = 4/15 + 3/15 = 7/15 - сумма чисел

4/15 - 1/5 = 4/15 - 3/15 = 1/15 - разность чисел