1.简便计算 1/2+1/6+1/12+1/20+1/30+1/42 3.65/0.25+1.35*4

=1/2+1/2*3+1/3*4+1/4*5+1/5*6+1/6*7
=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7
=1-1/7
=6/7
3.65/0.25+1.35*4
=3.65*4+1.35*4
=4*(3.65+1.35)
=4*5
=20