On Wednesday, Ivan read ³₈ of a non-fiction book. On Thursday, he read 25 pages of the non-fiction book. On Friday, he read ³₇ of the remaining book leaving 80 pages unread.

1. Find the number of pages read on Friday.
2. Find the total number of pages in the non-fiction book.

(a)
Number of remaining unread pages after reading on Thursday = 7 u

Number of remaining unread pages after reading on Friday
= 7 u - 3 u
= 4 u

4 u = 80

1 u = 80 ÷ 4 = 20

Number of pages that Ivan read on Friday
= 3 u
= 3 x 20
= 60

(b) 
Working backwards.

Number of pages unread after reading on Thursday
= 7 u
= 7 x 20
= 140

Total number of pages in the non-fiction book = 8 p

Number of pages unread after reading on Wednesday 
= 8 p - 3 p
= 5 p

5 p = 25 + 140
5 p = 165

1 p = 165 ÷ 5 = 33

Total number of pages in the non-fiction book
= 8 p
= 8 x 33
= 264

Answer(s): (a) 60; (b) 264