Giải thích các bước giải:
`1. a`) Ta có: `5/40 = 15/120`
`b`) Ta có: `24/36 = 2/3 = 22/33`
`6/11 = 18/33`
`c`) Ta có: `7/30 = 28/120`
`13/60 = 26/120`
`9/40 = 27/120`
`d`) Ta có: `17/60 = 51/180`
`5/18 = 50/180`
`23/90 = 46/180`
`2. a) 4/17 + 3/17 = (4 + 3)/17 = 7/17`
`b`) 3/8 + 5/12 = 36/96 + 40/96 = 76/96`
`c`) 1/9 + 2/9 + 1/3 = 1/9 + 2/9 + 3/9`
`= 6/9 = 2/3`
`d) 2 + 9/11 + 3/22 = 44/22 + 18/22 + 3/22 = 65/22`
`e) 3/2 + 5/4 + 9/8`
`= 12/8 + 10/8 + 9/8 = 30/8 = 15/4`
`g) 7/12 × 3/4 = 21/24 = 7/8`
`h) 15/8 × 2/5 = 30/40 = 3/4`
`i) 12/5 : 7/4 = 12/5 × 7/4 = 84/20 = 21/5`
`3. a) 45/135 + 12/24`
`= 1/3 + 1/2 = 5/6`
`b) 72/84 + 1011/7077 + 22/77`
`= 9/12 + 1/7 + 2/7`
= 72/84 + 12/7 + 24/7 = 108/7`
`c) 2323/2929 + 11/29 + 34/58`
`= 23/29 + 11/29 + 17/29`
`= 51/29`
`d) 13/15 + 1212/2020 + 212121/303030`
`= 13/15 + 3/5 + 7/10`
`= 130/150 + 90/150 + 105/150`
`= 325/150`
