Tính nhẩm:
a) 30000 + (20000 + 40000) = ..................
30000 + 20000 + 40000 = ..................
60000 - (30000 + 20000) = ..................
60000 - 30000 - 20000 = ..................
b) 40000 x 2 : 4 = ..................
36000 : 6 x 3 = ..................
20000 x 4 : 8 = ..................
60000 : 3 x 2 = ..................