Bài 2. Tìm x theo cách nhanh nhất: a) x : 7 = 920699 : 70 b) 5 × x 1952 = 2500 1947 c) x × 1999 x = 1999 × 1997 + 1999

a, `x : 7 = 920699 : 70`

`⇒ x : 7 = 920699 : 7 : 10`

`⇒ x = 920699 : 10`

`⇒ x = 92069,9`

b, `5 × x - 1952 = 2500 - 1947`

`⇒ 5 × x  = 2500 - 1947 + 1952`

`⇒ 5 × x  = 2505`

`⇒ x = 2505 : 5`

`⇒ x = 501`

c, `x × 1999 - x = 1999 × 1997 + 1999`

`⇒ x × (1999 - 1) = 1999 × (1997 + 1)`

`⇒ x × 1998 = 1999 × 1998`

`⇒ x = 1999`