Ratios and proportions

Question

The ratio of Juan's CDs to Angela's CDs was 7 to 3. After Juan gave 6 CDs to Angela, they had an equal number of CDs. How many CDs did Angela have at first? Explain and show how to reason about a strip diagram to solve this problem.

Answer 1

j/a = 7/3

(j-6)/(a+6) = 1

j-6 = a+6

j= a+12

(a+12)/a = 7/3

3a +36 = 7a

4a = 36

a = 9 CDs for angela at 1st

j = 21 for juan at 1st

21/9 = 7/3