15×43+85×44=15×(44-1)+85×44
=15×44-15×1+85×44
=44×(15+85)-15
=44×100-15
=4400-15
=4385
15×43+85×(43+1)
=15×43 + 【85×43 + 85×1】
=【15×43+85×43】+85
=43×(15+85)+85
=43×100+85
=4300+85
=4385