Question 10... The answer to this would be

. Dividing the cost by the number of apples

works out the cost per single apple. Then multiplying this value by

gives the cost of

apples.

For question 11, since 25% is a quarter of 100%, 12 students must be a quarter of the class. So to calculate the size of the class, simply do

.

Question 12... Okay, I'm not good at explaining things like this, and I'm not even sure my answer's right. All I did was

(this calculates the proportion of the graduating class that took 6 or 7 courses i.e. 15%), then I added this to the ones who did 8 or more maths courses, so 75% + 15% = 90%, meaning the remaining 10% must do fewer than 6 maths courses. So the answer's 10% I think.