А) 17/20 - х = 14/20 - 3/20
17/20 - х = 11/20
х = 17/20 - 11/20
х = 6/20
х = 3/10
Проверка: 17/20 - 6/20 = 14/20 - 3/20
11/20 = 11/20
б) 8/15 - 7/15 + у = 14/15
1/15 + у = 14/15
у = 14/15 - 1/15
у = 13/15
Проверка: 8/15 - 7/15 + 13/15 = 14/15
14/15 = 14/15
Думаю так 8•30=240 2•15=30 2•10•5=100 240-100-30=90
12-6=6
20-14=6
10-4=6
7-1=6
15-9=6
7 = 3+4, 2+5, 1+6;
10 = 5+5, 6+4, 3+7, 8+2, 1+9;
18 = 17+1 / 1+17;
24 = 23+1, 20+4, 21+3, 5+19, 8+16, 9+15, 18+6, 17+7, 14+10, 13+11, 12+12, 22+2.