1)7/15 - 3/40 - 1/24= 56/120 - 9/120 - 5/120 = 42/120= 21/60 = 7/20.
2)3/4 - 1 2/3 = 9/12 - 1 8/12 = 9/12 - 20/12 = -11/12.
3)2,4· 1/3 - 3 = 0,8 - 3 = - 2,2
4)4/9 - 5/12 + 75/100 = 4/9 - 5/12 + 3/4 = 48/108 - 45/108 + 81/108= 84/108 = 21/27
5)7/20:0,7 ·11/6 : (-11/12)·(-2,2)·5/11·21/27·3/7=
7/20 ·10/7 ·11/6 ·12/11·22/10·5/11·21/27 ·3/7=1/3