Выражением:
3/5 * (1/4 + 2/3) - 5/20 =
= 3/5 * (3/12 + 8/12) - 5/20 =
= 3/5 * 11/12 - 5/20 =
= (1*11)/(5*4) - 5/20 =
= 11/20 - 5/20 = 6/20 =
= 3/10 = 0,3
по действиям:
1) 1/4 + 2/3 = 3/12 + 8/12 = 11/12
2) 3/5 * 11/12 = (1*11)/(5*4) = 11/20
3) 11/20 - 5/20 = 6/20 = 3/10 = 0,3