A city has 3 new houses for every 9 old houses. If there are 15 new houses in the city, how many old houses are there?

45 old houses

Step-by-step explanation:

new houses : old houses

3 : 9

15 : ?

(3 = 1st ratio and 9 = 2nd ratio)

To find the missing ratio, divide the first ratio from the new ratio:

15 / 3 = 5

Take the product and multiply that by the second ratio to find the missing ratio:

9 x 5 = 45