1. Tìm y
76,22 - y × 3 = 30,61 × 2
76,22 - y × 3 = 61,22
y × 3 = 76,22 - 61,22
y × 3 = 15
y = 15 : 3
y = 5
2. Tính bằng cách thuận tiện
a) 38,25 - 18,25 + 21,64 - 11,64 + 9,93
= (38,25 - 18,25) + (21,64 - 11,64) + 9,93
= 20 + 10 + 9,93
= 39,93
b) 45,28 + 52,28 - 15,28 - 12,17
= (45,28 - 15,28) + (52,28 - 12,17)
= 30 + 40,11
= 70,11
c) (72,69 + 18,47) - ( 8,47 + 22,69)
= 72,69 + 18,47 - 8,47 - 22,69
= (72,69 - 22,69) + ( 18,47-8,47)
= 50+10
= 60