Bài 3 :
a) (28 x 9 - 190) x 25 – 2790 : 45
= ( 252 - 190 ) x 25 - 62
= 62 x 25 - 62
= 62 x 24
= 1488
b) 2459 x 8 – 8 x 2451 + 6
= 8 x ( 2459 - 2451 ) + 6
= 8 x 8 + 6 = 64 + 6 = 70
Bài 2
a) ( x - 1954 ) x 5 = 50
x - 1954 = 10
x = 10 + 1954 = 1964
Vậy x = 1964
b) [3 . (x + 2) : 7] x 4 = 120
( 3x + 6 ) : 7 = 30
3x + 6 = 210
3x = 204
x = 68
Vậy x = 68