Tính nhanh:

a, 40.113.25 – 20.112.50

b, 27 + 27.5 + 27.7 – 27.2

c, 754.75 – 25.2262 + 4568 

a) 815 – 23 – 77 +185 = (815 + 185) – (23+77) = 1000 – 100 = 900

b) 3145 – 246 + 2347 – 145 + 4246 – 347

= (3145-145) + (4246 – 246) + (2347 – 347)

= 3000 + 4000 + 2000 = 9000

c) (2018:1 – 2018.1):(2018.2008+2018.2002) = 0 : (2018.2008+2018.2002) = 0

d) (9 – 8 – 7 – 6 – … – 2 – 1).(500.9 – 250.18)

= (9 – 8 – 7 – 6 – … – 2 – 1).(500.9 – 250.2.9)

= (9 – 8 – 7 – 6 – … – 2 – 1).(500.9 – 500.9)

= (9 – 8 – 7 – 6 – … – 2 – 1).0 = 0

a, 165:11.999 + 85.999 = 15.999 + 85.999 = (15+85).999 = 99900

b, 25.4 + 25:5 – 4.(30 – 5) – 5 = 25.4 + 25:5 – 4.25 – 5 = (25.4 – 4.25) + (25:5 – 5) = 0 + 0 = 0