Question

1/4*1+1/4*7+1/7*10+1/10*13+1/13*16=?

Answer 1

1/4*1+1/4*7+1/7*10+1/10*13+1/13*16=(1/3)*[(1-1/4)+(1/4-1/7)+(1/7-1/10)+(1/10-1/13)+(1/13-1/16)]=(1/3)*(1-1/16)=(1/3)*(15/16)=3/16