A boy has 3 library tickets and 8 books of his interest in the library. Of these 8, he does not want to borrow Mathematics Part II, unless Mathematics Part I is also borrowed. In how many ways can he choose the three books to be borrowed?

Let us make the following cases: 

Case (i) Boy borrows Mathematics part II, then he borrows Mathematics part I also. So the number of possible choices is ⁶C₁ = 6.

Case (ii) Boy does not borrow Mathematics part II, then the number of possible choices is ⁷C₃ = 35.

Hence, the total number of possible choices is 35 + 6 = 41