3/1*2+3/2*3+3/3*4+……+3/99*100.如果写出以下两题,5/6+11/12+19/20+29/30+41/42=?（9又2/7+7又2/9）÷（5/7+5/9）=?

3/1*2+3/2*3+3/3*4+……+3/99*100
=3*[1/(1*2)+1/(2*3)+……+1/(99*100)
=3*[1-1/2+1/2-1/3+1/3-1/4+……+1/99-1/100]
=3*[1-1/100]
=3*99/100
=297/100
5/6+11/12+19/20+29/30+41/42
=[1-1/6+1-1/12+1-1/20+1-1/30+1-1/42]
=5-[1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7]
=5-[1/2-1/7]
=5-5/14
=4又9/14
（9又2/7+7又2/9）÷（5/7+5/9）
=(9+7+2/7+2/9)/(80/63)
=(16+32/63)*63/80
=63/5+2/5
=13 .

原式=3×(1-1/2+1/2-1/3+……+1/99-1/100)=3×(1-1/100)=297/100
原式=1-1/6+1-1/12+1-1/20+1-1/30+1-1/42=5-（1/2-1/3+1/3-1/4+……+1/6-1/7）=65/70
原式=(65/7+65/9)÷5÷(1/7+1/9)= 65*(1/7+1/9)÷5÷(1/7+1/9)= 13

1、原式=3×（1-1/2+1/2-1/3+……+1/99-1/100）=3×（1-1/100）=2.97
2、原式=1-1/6+1-1/12+1-1/20+1-1/30+1-1/42=5-（1/2-1/3+1/3-1/4+……+1/6-1/7）=4又9/14
3、原式=13