47分之6要写成6/47
6/47×48=6/47×（47+1）=6+6/47=6又47分之6或者=288/47
1/42÷（1/6+1/7）=42×1/42÷（1/6×42+1/7×42）=1÷（7+6）=1/13
1/2+1/6+1/12+……+1/90
=1/2+1/2-1/3+1/3-1/4+……+1/9-1/10
=1-1/10
=9/10