В)
1) 2 1/10 * 4 = 21/10 * 4= 42/5
2)19/20 * 10 = 19/2
3)42/5 + 19/2 = 84/10 + 95/10 =179/10
4)20 3/10 - 179/10 = 203/10 - 179/10=24/10=12/5
5)1 : 5 =1/5
6)12/5 : 1/5 = 12/5 * 5/1 = 12
ответ: 12
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г)
1) 4 2/5 + 7 7/15 = 4 6/15 + 7 7/15=11 13/15
2) 2 3/4 + 8 7/60= 2 45/60 + 8 7/60=10 52/60 =10 13/15
3) 11 13/15 - 10 13/15 = 1
4) 7 1/4 - 5 3/4 = 6 5/4 - 5 3/4 = 1 2/4 = 1 1/2
5) 1 : 1 1/2 = 1 : 3/2 = 2/3
ответ: 2/3