А) -3,15-(-4 1/2 + 3/4) Б) 5/6 * (-15,3 -24,3 *

Чтоб выполнить действия, сначала выполним деянья в скобках, а позже за скобками:

1. -3,15 - (-4 1/2 + 3/4) = 0,6;

1) 3/4 - 4 1/2 = 3/4 - 9/2 = 3/4 - 18/4 = -15/4 = -3 3/4 = -3 (3 * 25)/(4 * 25) = -3 75/100 = -3,75;

2) -3,15 + 3,75 = 0,6.

2. 5/6 * (-15,3 - 24,3 * 5/9) = 24;

1) 24,3 * 5/9 = 243/10 * 5/9 = (27 * 9 * 5)/(2 * 5 * 9) = 27/2 = 13 1/2 = 13,5;

2) -15,3 - 13,5 = -28,8;

3) 5/6 * (-28,8) = -288/10 * 5/6 = (2 * 24 * 6 * 5)/(5 * 2 * 6) = 24.

3. (2 7/15 - 4) * (8 16/23 - 10) = 2;

1) -(4 - 2 7/15) = -(4 - 2 - 7/15) = -(2 - 7/15) = -1 8/15;

2) -(10 - 8 16/23) = -(10 - 8 - 16/23) = -(2 - 16/23) = -1 7/23;

3) -1 8/15 * (-1 7/23) = 23/15 * 30/23 = (23 * 15 * 2)/(15 * 23) = 2. 

4. (-3/7 - 5/14 - 8/21) * 3/14 + 1/8 = -1/8;

1) -(3/7 + 5/14) = -(6/14 + 5/14) = -11/14;

2) -(11/14 + 8/21) = -(33/42 + 16/42) = -49/42;

3) -49/42 * 3/14 = (-49 * 3)/(14 * 3 * 14) = -49/196 = -1/4;

4) -1/4 + 1/8 = -2/8 + 1/8 = -1/8.

5. 1 1/3 * (-3/4) - (-2 1/7) * 1 2/5 = 2;

1) 1 1/3 * (-3/4) = 4/3 * (-3/4) = -1;

2) -2 1/7 * 1 2/5 = -15/7 * 7/5 = (-5 * 3 * 7)/(7 * 5) = -3;

3) -1 + 3 = 2.