5/12 а + 7; 2) 4/9 b + 2/3 при b = 6; 3) 2/5+1.1/4a при а = 2; 4) 2.3/10b+1/2 при b = 5

(5/12) а + 7 при а=4 4/9

то:

а=4 4/9 = (4*9+4) / 9=40/9

(5/12) (40/9) + 7 = (175/36) + 7=427/36 = 11 31/36

если так:

5 / (12 а) + 7 при а=4 4/9

то:

а=4 4/9 = (4*9+4) / 9=40/9

5 / (12*40/9) + 7 = (3/32) + 7=227/32 = 7 3/32

второй аналогично

4/9b+2/3≈4/9*6+2/3≈8/3+2/3≈10/3≈3 1/3

2/5+1 1/4a≈2/5+1 1/4*2≈2/5+5/2≈20/10≈2

2 3/10b+1/2≈2 3/10*5+1/2≈23/2+1/2≈24/2≈12