Bài 1: 
<math open="|" close="|"><mrow><mo>-</mo><mn>2015</mn></mrow></mfenced></math>; -11; -10; <math open="|" close="|"><mrow><mo>-</mo><mn>9</mn></mrow></mfenced></math>; 0; <math open="|" close="|"><mrow><mo>-</mo><mn>9</mn></mrow></mfenced></math>; 10; 12; 23.
Bài 2: 
a) 1125 - (374 + 1125) + (-65 + 374) = 1125 - 374 -1125 - 65 + 374 = (1125 - 1125) + (-374 + 374) - 65 = -65 
b) (-23).63 + 23.21 - 58.23 = 23[(-63)+21-58] = 23.(-100) = -2300
c) -2003 +  (-21 + 75 + 2003) = -2003 - 21 + 75 + 2003 = -21 + 75 = 54
d) 942 - 2567 + 2563 - 1942 = (942 - 1942) - 2567 + 2563 = -1000 - 4 = -1004
Bài 3:
a) 3x + 27 = 9
<math 3x = 9 - 27 
<math 3x = -18
<math x = -6
b) 2x + 12 = 3(x - 7)
<math 2x + 12 = 3x - 21
<math 2x - 3x = -21 - 12
<math -x = -33
<math x = 33
c) <math - 1 = 49 
<math  <math = 50
<math  <math = 25
<math x = 5