Question

42*（8分之1+24分之1+48分之1+80分之1+120分之1+168分之1）

Answer 1

42×(1/8+1/24+1/48+1/80+1/120+1/168)

=42×1/4×(1/2+1/6+1/12+1/20+1/30+1/42)

=42×1/4×(1/1*2+1/2*3+1/3*4+1/4*5+1/5*6+1/6*7)

=42×1/4×(1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7)

=42×1/4×(1-1/7)

=42×1/4×6/7

=9