The diagram gives the percentage of Pune college students who use Instagram, YouTube, both or neither. What percentage use only YouTube?

The four parts make 100%: $35+25+?+12=100$, so $?=28\%$. 53% is the whole YouTube circle $25+28$, 40% forgets the 12% who use neither, and 63% leaves out the Instagram-only part instead of the overlap.