`1)`

`5/9xx6/15=30/135=2/9`

`4/7:24/5=4/7xx5/24=5/42`

`6/11:4=6/11xx1/4=3/22`

`12xx19/18=12/1xx19/18=38/3`

`15 : 25/4=15/1xx4/25=12/5`

`1212/1515:2727/2525=1212/1515xx2525/2727=20/27`

`14/27 : 7/18 xx 6/5 +3/10=14/27xx18/7xx6/5+3/10=4/3xx6/5+3/10=8/5+3/10=16/10+3/10=19/10`

`2)`

`x : 5/4 = 9/5 + 1/2`

`x :5/4=18/10+5/10`

`x:5/4=23/10`

`x=23/10xx5/4`

`x=23/8`

`( x + 3/4 ) xx 5/7 = 10/9`

`x+3/4=10/9:5/7`

`x+3/4=10/9xx7/5`

`x+3/4=14/9`

`x=14/9-3/4`

`x=56/36-27/36`

`x=29/36`

`3)`

Nửa chu vi của mảnh giấy là :

`22/3:2=11/3(dm)`

Chiều dài mảnh giấy là :

`(11/3+1/2):2=25/12(dm)`

Chiều rộng mảnh giấy là :

`11/3-25/12=19/12(dm)`

Diện tích mảnh giấy là :

`25/12xx19/12=475/144(dm^2)`

`5/9`x`6/15`=(`5x6/9x15`)=`2/9`

`4/7`:`24/5`=`4/7`.`5/24`=(`4x24/7x5`)=`5/24`

`6/11`:4=`6/11`.`1/4`=(`6x1/11x4`)=`6/44`=`3/22`

`12`x`19/18`=(`12x19/18`)=`228/18`=`38/3`

`15`:`25/4`=`15x`4/25`=(`15x4/25`)=`60/25`=`12/5`

`1212/1515`:`2727/2525`=`4/5`:`27/25`=`4/5`.`25/27`=(`4x25/5x27`)=`100/135`=`20/17`

`14/27`:`7/18`x`6/5`+`3/10`=`14/27`.`18/7`x`6/5`+`3/10`=(`14x18/27x7`)x`6/5` +`3/10`=`252/189`x`6/5` +`3/10`=`4/3`x`6/5` +`3/10`

`4/3`x`6/5`+`3/10`=(`4x6/3x5`)x`6/5` +`3/10`=`24/15`x`6/5`+`3/10`=(`24x6/15x15`)+`3/10`

=`144/225`+`3/10`=`16/25`+`3/10`=`160/250`+`75/250`=`235/250`=`47/50`

2 tìm x

a)x:`5/4`=`9/5`+`1/2`

x:`5/4`=`23/10`

x=`23/10`.`5/4`

x=`23/8`

b)(x+`3/4`)x`5/7`=`10/9`

x+`3/4`=`10/9`:`5/7`

x+`3/4`=`14/9`

x=`14/9`-`3/4`

x=`29/36`

3 giải

nữa chu vi hình chũ nhật là:

`22/3`:2=`11/3`(dm)

chiều dài rộng là:

`11/3`-`1/2`=`19/6`(dm)

chiều dài là:

`11/3`+`1/2`=`25/6`(dm)

diện tích hình chữ nhật là

`19/6`x`25/6`=`475/36`(dm²)

D/S:`475/36`dm²