a) - 12 + (- 15 + 23) = - 12 + 8 = - 4
b) - 7 + 11 - (- 15) = 4 + 15 = 19
c) - 1 :3 + 1 : 2 = - 1/3 + 1/2 = - 2/6 + 3/6 = 1/6
d) - 2 : 5 - 7 : 3 = - 2/5 - 7/3 = - 6/15 - 35/15 = - 41/15
e) (- 4) * (- 15 + 17) = - 4 * 2 = - 8
f) - 2 * 2(- 7 + 12) = - 2 * 2 * 5 = - 20
g) 2 * 1 :3 * 5 * (2 * 3 + 13) = 10/3 * 19 = 190/3 = 63,(3)
h) 2 : 7 + 2 - 4 : 3 = 2/7 + 2 - 4/3 = 6/21 + 42/21 - 28/21 = 20/21