Tính nhanh: a) 81 + 243 + 19 b) 134 + 237 + 166 + 563 c) 15.7.20 d) 8.12.125.4

a) 81 + 243 +19 = (81 + 19) + 243 = 100 + 243 = 343

b) 134 + 237 + 166 + 563 = (134 + 166) + (237 + 563) = 300 + 800 = 1100

c) 15.7.20 = (15.20).7 = 300.7 = 2100

d) 8.12.125.4 = (8.125).(12.4) = 1000.48 = 48000