Question

简算:20分之1加30分之1加42分之1加56分之1加72分之1

Answer 1

1/20+1/30+1/42+1/56+1/72

=(1/4--1/5)+(1/5--1/6)+(1/6--1/7)+(1/7--1/8)+(1/8--1/9)

=1/4--1/9

=9/36--4/36

=5/36.