А) 24 4/5 - 19,5 : 7 2/9 б ) 2,4+

Выполним действия:

1. 24 4/5 - 19,5 : 7 2/9 = 22,1;

1) 19,5 : 7 2/9 = (19 * 10 + 5)/10 : (9 * 7 + 2)/9 = 195/10 : 65/9 = 195/10 * 9/65 = (195 * 9)/(10 * 65) = (3 * 65 * 9)/(10 * 65) = (3 * 9)/10 = 27/10 = 2 7/10;

2) 24 4/5 - 2 7/10 = 24 - 2 + 4/5 - 7/10 = 22 + 8/10 - 7/10 = 22 + (8 - 7)/10 = 22 + 1/10 = 22,1.

2. 2,4 + 5,6 * (13 3/4 - 12 13/14) = 7;

1) 13 3/4 - 12 13/14 = 13 - 12 + 3/4 - 13/14 = 1 + (3 * 7)/28 - (13 * 2)/28 = 1 + (21 - 26)/28 = 1 - 5/28 = 28/28 - 5/28 = 23/28;

2) 5,6 * 23/28 = 56/10 * 23/28 = (28 * 2 * 23)/(2 * 5 * 28) = 23/5 = 4 3/5 = 4 6/10 = 4,6;

3) 2,4 + 4,6 = 7.