№869 (а)
(3/4 + 1/6) * 3 + (5/6 - 1/2) : 2/9 = 4целых 1/4
1) 3/4 + 1/6 = 9/12 + 2/12 = 11/12
2) 11/12 * 3 = 33/12
3) 5/6 - 1/2 = 5/6 - 3/6 = 2/6 = 1/3
4) 1/3 : 2/9 = 9/6
5) 33/12 + 9/6 = 33/12 + 18/12 = 51/12 = 4целых 3/12 =4целых 1/4
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№870(а)
1) 7/15 + 7/30 + 4/5 = 14/30 + 7/30 +24/30 = 45/30 = 3/2
2) 2 - 1/3 - 1/2 = 1ц.2/3 - 1/2 = 5/3 - 1/2 = 10/6 - 3/6 = 7/6
3) 3/2 : 7/6 = 18/14 = 9/7 = 1целая 2/7