This will have same approach as https://www.beatthegmat.com/how-to-resol ... 56750.html

from 1 we cannot conclude anything
from 2 12 are taking math hence 20-12=8 are taking only physics as all students are taking at least one subject
hence 16-8=8 are taking both physics and math

Ans B

So the formula is

(physics only +both) +(Math only +both) -Both=20

Statement 1 says 10 are taking physics only - so we know that at most 10 students can be taking both but we don't know how many.

Insufficient - BCE

Statement 2 says 12 are taking math and 20 are taking physics - because it doesn't say only we know that physics only +both=16 and math+both=12 - this is enough to solve the above equation for the number of students taking both.

B