а) 2 9/10-(1 2/5+3/10)+7/20=29/10-7/5-3/10+7/20=58/20-28/20-6/20+7/20=31/20= 1 11/20
б)4-(41/84-5/21)+7 11/30= 4 - 41/84 + 5/21 + 221/30= 1680/420 - 205/420 + 100/420 + 3094/420= 4669/420 = 11 49/420 = 11 7/60
2 9/10-(1 2/5+3/10)+7/20=2 9/10-1 7/10 +7/20=1 2/10+7/20=1 4/20+7/20=1 11/20
4-(41/84-5/21)+7 11/30=4- 21/84+7 11/30=4 - 3/12+7 11/30=4-1/4+7 11/30=3 3/4+7 11/30=15/4+221/30=225/60+442/60=667/60=11 7/60
