Great question Kevin,

Here is the way to solve such questions:

Let the two prime numbers be x and y.

Question is : xy - (x+y) = ? or xy -x -y +1 -1 (adding 1 and -1 = 0)

Or in another words

=> (1-x) * (1-y) -1

=>Since x and y both are prime numbers (x-1) and (y-1) is going to be an even number.

=>x-1 and y-1 product is also going to be an even number

=> Even * Even is always divisible by 4, so the question is asking which number from all the options when divided by 4 gives remainder 3 (as there is a -1 in [(1-x)*(1-y) -1]), the only option is 119 as its one short of 120 and is completely divisible by 4.

So the answer is 119. (3)