Question

1/2X4+1/4X6+1/6X8+1/8X10+1/10X12=

1/2X4+1/4X6+1/6X8+1/8X10+1/10X12=
1-5/6+7/12-9/20+11/30=
两题简便计算，要过程。

Answer 1

1/2X4+1/4X6+1/6X8+1/8X10+1/10X12==(1/2-1/4+1/4-1/6+1/6-1/8+1/8-1/10+1/10-1/12)÷2
=（1/2-1/12）÷2=5/12÷2=5/24
1-5/6+7/12-9/20+11/30

=1/6+7/12-9/20+11/30
=(1/2-1/3)+(1/3+1/4)-(1/4+1/5)+(1/5+1/6)
=1/2+1/6
=2/6=1/3
这里：
1/6=1/2-1/3
7/12=1/3+1/4
9/20=1/4+1/5

Answer 2

Answer 3

1/2X4+1/4X6+1/6X8+1/8X10+1/10X12
=(1/2-1/4+1/4-1/6+1/6-1/8+1/8-1/10+1/10-1/12)÷2
=（1/2-1/12）÷2
=5/12÷2
=5/24

Answer 4

(1)
1/2X4+1/4X6+1/6X8+1/8X10+1/10X12

=(1/2)(1/2-1/4+1/4-1/6+1/6-1/8+1/8-1/10+1/10-1/12)
=(1/2)(1/2-1/12)
=(1/2)*(5/12)
=5/24
(2)
1-5/6+7/12-9/20+11/30

=1-(1/2+1/3)+(1/3+1/4)-(1/4+1/5)+(1/5+1/6)
=1-1/2+1/6
=1/2+1/6
=3/6+1/6
=4/6
=2/3

Answer 5

1/(2x4)+1/(4x6)+1/(6x8)+1/(8x10)+1/(10x12)
=(1/2)[(1/2 -1/4) +(1/4-1/6)+(1/6-1/8)+(1/8-1/10)+(1/10-1/12)]
=(1/2)( 1/2 - 1/12)
=(1/2) (5/12)
=5/24

1-5/6+7/12-9/20+11/30

=1- (1/2+1/3) +(1/3+1/4) -(1/4+1/5) +(1/5+1/6)
=1-1/2 +1/6
=2/3