78*31+23*31-31用乘法分配律

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78*31+23*31-31用乘法分配律78*31+23*31-31用乘法分配律78*31+23*31-31用乘法分配律78*31+23*31-31=78*31+23*31-1*31=(78+23-1

78*31+23*31-31用乘法分配律
78*31+23*31-31用乘法分配律

78*31+23*31-31用乘法分配律
78*31+23*31-31
=78*31+23*31-1*31
=(78+23-1)*31
=100*31
=3100

78*31+23*31-31
=31x(78+23-1)
=31x100
=3100

78*31+23*31-31
=31*(78+23-1)
=31*100
=3100

78×31+23×31-31×1