Giúp mình bài 5 nhanh với ạ. Mình cảm ơn

`a) 120 × 2/5 + 120 × 3/4 + 120×1 `

`= 120 × ( 2/5 + 3/4 +1)`

`= 120 × ( (2×4)/(5×4) + (3×5)/(4×5) + (1×20)/(1×20))`

`= 120 × ( 8/20 + 15/20 +20/20)`

`= 120 × 43/20`

`= 120/1 × 43/20`

`= (120×43)/(1×20)`

`= 5160 /20`

`= (5160:20)/(20:20)`

`= 258/1`

`= 258`

`b) 1/5 × 3/4 + 1/5 × 5/4 -1/5`

`= 1/5 × ( 3/4 + 5/4 -1)`

`= 1/5 × ( 8/4 -1)`

`= 1/5 × ((8:4)/(4:4) -1)`

`= 1/5 × ( 2-1)`

`= 1/5×1`

`= 1/5`

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