1/4(2a-4)-1/3(5b+6) = 1/2а-1-5/3b-2 = 0,5a-5/3b-3

при a=2 1/2, b=13:

1/2 × 5/2 - 5/3×13 - 3 = 5/4-65/3-3 = 15/12-260/12-3 = -245/12 - 3 = -281/12 = -23 5/12