Câu 1 : thực hiện phép tính (tính hợp lý nếu có thể) : a, 2/5+4/7+3/5+3/7

B, 5/8 ✖ 7/3- 1/4 ✖ 7/3

C, 16.(3/20- 2/5^2+3/5

Bài 2 : tìm x biết :

A, x- 2/3=5/6

B, 1/4 ✖ x-3/4=1/2

Đáp án + Giải thích các bước giải:

`a) 2/5 + 4/7 + 3/5 + 3/7` $\\$ `= (2/5 + 3/5) + (4/7 + 3/7)` $\\$ `= 5/5 + 7/7` $\\$ `= 1 + 1` $\\$ `= 2`

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`b) 5/8. 7/3 - 1/4 xx 7/3`

`= 7/3. (5/8 - 1/4)`

`= 7/3. 3/8`

`= 7/8`

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`c) 16. [3/20 - (2/5)^2 + 3/5]` $\\$ `= 16. (3/20 - 4/25 + 3/5)` $\\$ `= 16. (15/100 - 16/100 + 60/100)` $\\$ `= 16. 59/100` `= 944/100` `= 236/25`

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`x - 2/3 = 5/6`

`x = 5/6 + 2/3`

`x = 3/2`

Vậy: `x = 3/2`

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`1/4 xx x - 3/4 = 1/2`

`1/4 xx x = 1/2 + 3/4`

`1/4 xx x = 5/4`

`x = 5/4 : 1/4`

`x = 5`

Vậy: `x = 5`