Tính nhanh : a) 55 + 56 + 57 + 58 – 35 – 36 – 37 – 38. b) (461 – 78 + 40) – (461 – 78 – 60). c) –323 + 874

Câu 35: Tính nhanh :

a) 55 + 56 + 57 + 58 – 35 – 36 – 37 – 38.

b) (461 – 78 + 40) – (461 – 78 – 60).

c) –323 + 874 – (874 – 324 – 241).

Trả lời

a) 55 + 56 + 57 + 58 – 35 – 36 – 37 – 38

= (55 – 35) + (56 – 36) + (57 – 37) + (58 – 38)

= 20 + 20 + 20 + 20

= 80.

b) (461 – 78 + 40) – (461 – 78 – 60)

= 461 – 78 + 40 – 461 + 78 + 60

= (461 – 461) + (78 – 78) + (40 + 60)

= 0 + 0 + 100

= 100.

c) –323 + 874 – (874 – 324 – 241)

= –323 + 874 – 874 + 324 + 241

= (–323 + 324) + (874 – 874) + 241

= 1 + 0 + 241

= 242.