Ricardo has read 2/3 of a book. lin had read 2/4 of the same. who has read more of the book?

Ricardo, because 2/3 > 2/4.
This is because if you divide 2 by 3, you get 0.666. If you divide 2 by 4, you get 0.5
if you multiply both by 10, you get the percentile, in which case Ricardo has read 66% and Lin has read 50%. :)