24×205
=24×(200+5)
=4800+120
=4920
672‐36﹢64
=672+(64-36)
=672+28
=700
25+75‐25+75
=75+75+25-25
=75+75
=150
5+263+55-198
=268-198+55
=70+55
=125
87-187-139-61
=87-187-(139+61)
=-100-200
=-300
1280÷16÷8
=1280÷(16×8）
=1280÷128
=10
8×125 =1000
（125+70）×8
=125×8+70×8
=1000+560
=1560
4004×25
=(4000+4)×25
=100000+100
=100100