Ben can write 153 letters in 3 minutes. At this rate, how many letters can he write in 10 minutes?

Ben can write 153 letters in 3 minutes. At this rate, how many letters can he write in 10 minutes?

We set up a proportion of letters to minutes where the number of letters in 10 minutes is l:
153/3 = l/10

We type this proportion into a search engine and we get:
l = 510