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-1 15/77

Пошаговое объяснение:

1) 8/25 + 9/20 = 32/100 + 45/100 = 77/100

2) 21/25 : 77/100 = 21/25 * 100/77 = 12/11 = 1 1/11

3) 64/35 * 5/4 = 16/7 = 2 2/7

4) 1 1/11 - 2 2/7 = 1 7/77 - 2 22/77 = -1 15/77