Question

If "a" pens cost "b" dollars, how many dollars would "c" pens cost at the same rate?

Answer 1

a pens: b dollars

a/a pens: b/a dollars ... Divide both parts by 'a'

1 pen: b/a dollars

Answer 2

so far we just found out that 1 pen costs b/a dollars

Answer 3

multiply both parts by c to get

1 pen: b/a dollars

c*1 pen: c*b/a dollars

c pens: bc/a dollars

Answer 4

so c pens cost bc/a dollars