There would be a 65% chance of picking a customer who orders one or the other.
Step-by-step explanation:
In order to find this, we first must find the percentage that orders only pizza. We can do this by subtracting the overlap from the total number.
75% - 15% = 60%
We need to do the same thing for salad.
20% - 15% = 5%
Now that we have the percentages who ordered just one or the other, we can add them together to get the total percentage who got either one or the other.
11 is one of the factors! The orange divisor(s) above are the prime factors of the number 990. If we put all of it together we have the factors 2 x 3 x 3 x 5 x 11 = 990.