On Monday, Nora read ¼ of the book, therefore she is left with ¾ of the original book.
Then on Tuesday, she read 2/5 of what was left on Monday therefore she is left with 3/5 of ¾ of the original book. This is equal to:
(3/5) (3/4) = 9/20
She still needs to read 9/20 of the book or 0.45 or 45% of the book.