1/4×5+1/5×6+1/6×7+1/7×8=
问题描述：
1/4×5+1/5×6+1/6×7+1/7×8=
答
=5/4+6/5+7/6+8/7=4.759
答
1/n*(n+1)=1/n-1/(n+1)
所以1/4×5+1/5×6+1/6×7+1/7×8
=1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8
=1/4-1/8
=1/8
答
4(319/420)
答
1/4*5=1/4-1/5
1/5*6=1/5-1/6
所以上式化为1/4-1/8=1/8
答
1/4×5+1/5×6+1/6×7+1/7×8
=1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8
=1/4-1/8
=1/8
答
出的有歧义啊 像1/4*5是1除以20的意思 还是1/4在乘以5的意思呢 不严谨