Question

急求！一道小学六年级简便运算！

是分数形式的。
1/4×5+1/5×6+1/6×7+……1/39×40

Answer 1

1/4×5+1/5×6+1/6×7+……1/39×40
=(1/4-1/5)+(1/5-1/6)+(1/6-1/7)+.....+(1/39-1/40)
=1/4-1/5+1/5-1/6+1/6-1/7+.....+1/39-1/40
=1/4-1/40
=9/40

Answer 2

1/4×5+1/5×6+1/6×7+……1/39×40
=(1/4-1/5)+(1/5-1/6)+...+(1/39-1/40)=1/4-1/40=9/40