Bài 1:
a) 124 + 60 + 376 + 240
= ( 124 + 376 ) + ( 60 + 240 )
= 500 + 300
= 800
b) 84 : 4 + 3^9 : 3^7 + 5^0
= 21 + 3^2 + 1
= 21 + 9 + 1
= 31
c) 17 . 75 + 17 . 25 - 125
= 17 . ( 75 + 25 ) - 125
= 17 . 100 - 125
= 1700 - 125
= 1575
d) |-35| - {12 - [(-14) + (-2)]}
= 35 - [ 12 - ( -14 - 2) ]
= 35 - ( 12 + 16 )
= 35 - 28
= 7
Bài 2:
a) 98 - (x + 4) = 20
<=> x + 4 = 98 - 20
<=> x + 4 = 78
<=> x = 78 - 4
<=> x = 74
b) | x | - 5 = 7
<=> | x | = 7 + 5
<=> | x | = 12
<=> x = 12 hoặc x = -12