since 15 of them take both classes and you want to find the ones that take none of then you want to subtract 15 from both the 60 and the 35, then add those sums to get 55, then you want to subtract 55 from 90 to get your final answer. 35 students don't take any of the classes
Step-by-step explanation: Well first you know 15 take both so you can just subtract 15 from one of the numbers because the same student does not need to be counted twice. I chose to do 35-15 which equals 20. Then you do 60+20 to get 80. Lastly you subtract 80 from 90 to get 10.
I'm gonna go ahead and say I may not be correct because I don't know everything, but I answered to my best ability and got 10.
