In solving this problem, I used the formula for inclusion-exclusion from the quant mountain: Total=A+B-Both.
In the solution, Greg uses the formula: Total=A+B+Both.
I cannot wrap my head around the reasoning. Any help would be greatly appreciated.
Where?
In the formulas he set up, he has A and C as students in chemistry and biology, respectively. He uses B for students who take both.
Refer to his use of the inclusion-exclusion principle by writing: a+b+c=120
Quant mountain states formula should be: a-b+c=120.
No explanation for this discrepancy in the solution video.
Thanks.
And that is because this is not the generic inclusion-exclusion formula. Look carefully at what a, b and c in this question are, and what the inclusion-exclusion formula says.