Đáp án: + Giải thích các bước giải:

Câu `2` :

`15xx2121/4343+15xx222222/434343`

`=15xx21/43+15xx22/43`

`=15xx(21/43+22/43)`

`=15xx43/43`

`=15xx1`

`=15`

`(16xx25+44xx100)/(29xx96+142xx48)`

`=(4xx100+44xx100)/(29xx96+71xx96)`

`=(100xx(4+44))/((29+71)xx96)`

`=(100xx48)/(100xx96)`

`=4800/9600=1/2`

`1/2xx12/13+1/3xx12/13+1/4xx12/13`

`=(1/2+1/3+1/4)xx12/13`

`=(6/12+4/12+3/12)xx12/13`

`=13/12xx12/13`

`=156/156=1`

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

`=1/2xx2/3xx3/4xx4/5`

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

`=1/5`

`1 ) 15 xx 2121/4343 + 15 xx 222222/434343`

` = 15 xx 21/43 + 15xx  22/43`

`= 15 xx ( 21/43 + 22/43 )`

`= 15 xx 43/43`

`= 15 xx1`

`= 15`

`b ) (16xx 25 + 44 xx 100 ) / ( 29 xx 96 + 142 xx 48)`

`= 4800 / 9600`

`= 1/2`

`3 ) 1/2 + 12/13 + 1/3 xx 12/13 + 1/4 xx 12/13`

`= ( 1/2 + 1/3 + 1/4 ) xx 12/13`

`=  ( 6+ 4 + 3 ) /12 xx 12/13`

`= 13/12 xx 12/13`

`= 1`

`4 )  ( 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`

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

`= 1/5`