2 18/31 * а - 2,75 : b при a = 12,4; b = 4 5/7
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2 18/31 * 12,4 - 2,75 : 4 5/7 = 31 целая 5/12
1) 80/31 * 12,4 = 80 * 12,4 : 31 = 32
2) 2 3/4 : 33/7 = 11/4 * 7/33 = (1*7)/(4*3) = 7/12
3) 32 - 7/12 = 31 12/12 - 7/12 = 31 5/12
Пояснения:
2 целых 18/31 = (2*31+18)/31 = 80/31
2,75 = 2 целых 3/4 = (2*4+3)/4 = 11/4
4 целых 5/7 = (4*7+5)/7 = 33/7