Question

tính bằng cách thuận tiện:

a, (1- 1/2) x (1-1/3) x ( 1-1/4) x (1-1/5)

b. 3/5 x 3/4 + 1/5 x 3/4

c. 5/6 : 7/8 - 1/4 : 7/8

Answer 1

`(1-1/2) xx(1-1/3)xx(1-1/4)xx(1-1/5)`

`=(2/2-1/2)xx(3/3-1/3)xx(4/4-1/4)xx(5/5-1/5)`

`=1/2xx 2/3 xx 3/4 xx 4/5`

`=(1xx2xx3xx4)/(2xx3xx4xx5)`

`=1/5`

_____________________________

`3/5 xx 3/4+1/5 xx 3/4`

`=3/4xx(3/5+1/5)`

`=3/4 xx 4/5`

`=(3xx4)/(4xx5)`

`=3/5`

_________________________

`5/6:7/8-1/4:7/8`

`=5/6 xx 8/7-1/4 xx 8/7`

`=8/7 xx (5/6-1/4)`

`=8/7 xx 7/12`

`=2/3`

Answer 2

`a) ( 1 - 1/2) xx ( 1 - 1/3) xx ( 1 - 1/4) xx ( 1 - 1/5)`

`= 1/2 xx 2/3 xx 3/4 xx 4/5`

`= (1xx2xx3xx4)/(2xx3xx4xx5)`

`= (1xx1xx1xx1)/(1xx1xx1xx5)`

`= 1/5`

`b) 3/5 xx 3/4 + 1/5 xx 3/4 `

`= 3/4 xx ( 3/5 + 1/5 )`

`= 3/4 xx 4/5`

`= 3/5`

`c) 5/6 : 7/8 - 1/4 : 7/8`

`= ( 5/6 - 1/4 ) : 7/8`

`= 7/12 : 7/8`

`= 2/3`