in a class of 80 student every student had to study f/m or geography or both. if 65 studies f/m and 50 geography how many student studies both subject

Answer 1

f/m or geography or both=geography +f/m -both
80=50+65-both
both=115-80=35
These are incredibly easy with drawing a Venn Diagram. https://www.gliffy.com/blog/how-to-draw-a-venn-diagram