(1/3+1/5)×15
=1/3×15+1/5×15
=5+3
=8
(1/9+1/3)×27
=1/9×27+1/3×27
=3+9
=12
(1/6+1/4)×36
=1/6×36+1/4×36
=6+9
=15
89×7/88
=(88+1)×7/88
=7+7/88
=7又7/88
(1/3+1/5)×15=5+3=8
(1/9+1/3)×27=3+9=12
(1/6+1/4)×36==6+9=15
89×7/88=(88+1)×7/88=7+×7/88=7又×7/88
直接去括号,如第一道(1/3+1/5)x15=(1/3)x15+(1/5)x15=5+3=8,同理,9+3=12,6+9=15
(1/3+1/5)×15=1/3×15+ 1/5×15=5+3=8
(1/9+1/3)×27=1/9×27+1/3×27=3+9=12
(1/6+1/4)×36=1/6×36+1/4×36=6+9=15
89×7/88=(88+1)×7/88=88×7/88+1×7/88=7+7/88=7又 7/88