Answer: 13/60 of the novel is left unread.
Step-by-step explanation:
The whole novel is assumed as 1.
He finished 1/4 of the whole novel in first day. 1/3 of the whole novel in the second day and 1/5 of the whole in the third day. This means that the total portion of the novel that he read in 3 days is
1/4 + 1/3 + 1/5 = (15 + 20 + 12 )/60 = 47/60
The part of the novel that is left unread after three days would be
1 - 47/60 = (60 - 47)/60 = 13/60
