Tính nhanh a) 53.39 +47.39 – 53.21 – 47.21. b)2.53.12 + 4.6.87 – 3.8.40; c) 5.7.77 – 7.60 + 49.25 – 15.42.

 

Giải thích các bước giải:

a)$ 53.39 +47.39 – 53.21 – 47.21$

=$53.(39-21) - 47.(39-21)$

=$53.18 +47 .18$

=$18.(53+47)$

=$18.100$

=$1800$

b)$2.53.12 + 4.6.87 – 3.8.40$

= $24.53+24.87-24.40$

= $24( 53+87-40)$

= $24.100$

=$2400$

c,$5.7.77-7.60+49.25-15.42$

=$5.7.77-7.60+7.7.25-15.7.6$

=$7.(5.77-60+7.25-15.6)$

=$7.(385-60+175-90)$

=$7.(385+175-60-90)$

=$7.(560-150)$

=$7.410$

=$2870$