Let's put this in numbers! If Henry had a 1/5 (p=1/5) chance of winning the raffle, then in order to find that chance he will not win is easy! We would do 1-1/5. So if we go back to the problem with the variable p, we can see tha the answer is 1-p.
If it is in fraction you could do 5/1500 and reduce it to 1/300 , to change 1/300 to whole number it would be 3 , to change 1/300 to decimal it would be .03
