The difference is the result of a subtraction problem.
We are given two values that are being subtracted: 54 and a number, represented by 
So, represent this mathematically with 
.
Answer:
Let v = ml of 100% vinegar
Then 150-v = ml of dressing
v + .05(150-v) = .24(150)
v + 7.5 - .05v = 36
.95v = 28.5
v = 28.5/.95
v = 30 ml of vinegar
dressing = 150-30 = 120 m
P(s) = 45/125 = 0.360
P(A&C) = 38/125 = 0.304
Probability that one is not in Arts and Crafts = 1- P(A&C) = 1-0.304 = 0.696
Therefore,
Probability that the child selected is in swimming when its known they didn't sign for Arts and craft = Probability they signed for swimming * Probability that they didn't sign for Arts and Crafts = 0.360*0.696 = 0.25056
