Answer:
You will catch up by Wednesday.
Explanation:
Lets start by finding a measure of rate, in pages/day, for the two friends, F1(you) and F2.
F2 reads 20 pages/day
F1 (you) reads 25 pages/day
The number of pages read by both in x days is:
F1(x) = (25pages/day)*x
F2(x) = (20pages/day)*x
Let Sunday be day 1, so x = 1
Since F2 started a day earlier (Saturday) we need to add 20 pages to his total:
F2(x) = (20pages/day)*x + 20 pages
We want to know on what day you (F1) catch up to F2, so set the two expressions equal to each other:
F1 = F2
(25pages/day)*x = (20pages/day)*x + 20 pages
Solve for x, the day for which both F1 and F2 have read the same number of pages.
5(pages/day)x = 20 pages
x = (20 pages)/(5 pages/day)
Pages cancels and days moves to the top:
x = 4 days
Since x = 0 is a Saturday, x = 4 is a Wednesday.
On Wednesday you (F1) will catch up.