Becky read 10 books in 4 days. Sarah read 50 books in 20 days. Are the two girls reading at the same rate?

What we want to do is to put them both into books read per day.

Becky reads 10/4 books, if you do time/quantity, and similarly Sarah reads 50/20.

If we simplify both, 10/4 = 5/2 and by the same token 50/20 = 5/2.

Thus the answer is YES.