Đáp án`+`Giải thích các bước giải:

`35) (x + 1) + (x + 3) + (x + 5) + ... + (x + 99) = 10000` (50 số)

`x . 50 + (1 + 3 + 5 + ... + 99) = 10000`

`x . 50 + [(99 + 1) . 50 : 2] = 10000`

`x . 50 + 2500 = 10000`

`x . 50             = 7500`

`x                    = 150`

Vậy `x = 150`

`36) (x + 1) + (x + 4) + (x + 7) + ... + (x + 28) = 155` (10 số)

`x . 10 + (1 + 4 + 7 + ... + 28) = 155`

`x . 10 + [(28 + 1) . 10 : 2] = 155`

`x . 10 + 145 = 155`

`x . 10             = 10`

`x                    = 1`

Vậy `x = 1`

`37)` ($\dfrac{1}{1 x 2}$ + $\dfrac{1}{2 x 3}$ + $\dfrac{1}{3 x 4}$ + ... + $\dfrac{1}{19 x 20}$) `. x = 19`

`(1 - 1/2 + 1/2 - 1/3 + 1/3 - 1/4 + ... + 1/19 - 1/20) . x = 19`

`(1 - 1/20) . x = 19`

`19/20 . x = 19`

`x = 20`

Vậy `x = 20`

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