Bài 1
a) $A = 625 - (61 - 17) . 12 + (27 + 27) : 18$
$= 625 - 12.44 + 54:18$
$= 625-528+3 = 100$
b) $B = -126 - (4^2-5)^2 + 870:29$
$= -126 - 11^2 +30$
$= -96 - 121 = -217$
Bài 2
a) Ta có
$7^2 . 5 - (2x+1) = 630:9$
$<-> 49.5 - (2x+1) = 70$
$<-> 2x+1 = 49.5 - 70$
$<-> 2x+1 = 175$
$<-> 2x = 174$
$<-> x = 87$
b) Ta có
$(10-4x) + 120:2^3 = 17$
$<-> 10-4x + 15 = 17$
$<-> 10-4x = 2$
$<-> 4x = 8$
$<-> x = 2$
Bài 3
Ta có
$(x+1) + (x+2) + \cdots + (x+9) + (x+10) = 5$
$<-> x . 10 + (1 + 2 + \cdots + 10) = 5$
Ta có
$1 + 2 + \cdots + 10 = \dfrac{10.11}{2} = 55$
Suy ra
$10x + 55 = 5$
$<-> 10x = -50$
$<-> x = -5$
