Answer:
He was supposed to read the book in 10 days.
Step-by-step explanation:
Let d = number of days he should have taken to read the book.
He should have read 40 pages per day for d days. That means 40d number of pages.
He read 15 pages per day less than he should have, so he read 40 - 15 = 25 pages per day. He took an extra 6 days, so he took d + 6 number of days. Reading 25 pages per day for d + 6 days, he read a total of 25(d + 6) pages.
The number of pages of the book is the same either way, so
40d = 25(d + 6)
40d = 25d + 150
15d = 150
d = 10
Answer: He was supposed to read the book in 10 days.
Check:
He should have done this: 10 days at 40 pages/day = 400 pages.
He did this: 40 - 15 = 25 pages/day; 10 days + 6 days = 16 days.
16 days at 25 pages/day = 400 pages.
Since we get the same number of pages both ways, the answer is correct.
