3/1*2+3/2*3+3/3*4+……+3/99*100.
6个回答

=3*(1-1/2+1/2-1/3+……+1/99-1/100)

=3*(1-1/100)

=3*(99/100)

=297/100

=2.97

第2题

=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-(5/14)

=65/14

第3题

=(65/7+65/9)÷(5/7+5/9)

=65*(1/7+1/9)÷5(1/7+1/9)

=13 应该是这样呵呵,我好想看到过