487-187-139-61=?300-123-77-75=?3200/4/25=?72*125=?运用减法交换乘法分配律除法结合律简便计算律

Question

487-187-139-61=?300-123-77-75=?3200/4/25=?72*125=?运用减法交换 乘法分配律 除法结合律 简便计算律

Answer 1

487-187-139-61
=487-187-(139+61)
=300-200
=100
_____________________
300-123-77-75
=300-(123+77)-75
=300-200-75
=25
___________________
3200/4/25
=3200/(4*25)
=3200/100
=32
_________________________
72*125
=72*100+72*20+72*5
=7200+1440+360
=7200+1800
=9000