Bài 1:
a/ (13 + 49) - (13 - 135 + 49) = 13 + 49 - 13 + 135 - 49 = (13 - 13) + (49 - 49) + 135 = 135
b/ [93 - (20 - 7)] : 16 = [93 - 13] : 16 = 80 : 16 = 5
c/ 5/7 . 2/11 + 5/7 . 12/11 - 5/7 . 7/11 = 5/7 . (2/11 + 12/11 - 7/11) = 5/7 . 7/11 = 5/11
d/5/13 + 5/7 + -20/41 + 8/13 + -21/41 = (5/13 + 8/13) + [-20/41 + (-21/41)] + 5/7 = 1+(-1) +5/7=5/7
Bài 2:
a/ 3.x + 17 = 92 b/ -5/8 = x/16
3.x = 92 - 17 ⇒ 8.x = -5 . 16
3.x = 75 8.x = -80
x = 75 : 3 x = -80 : 8
x = 25 x = -10