Math ratio Primary 6

Question

Bob had some blue balloons and green balloons in the ratio 4 : 5. He gave away 12 blue balloons and 12 green balloons. Then the ratio of the number of blue balloons to the number of green balloons he had left because 5 : 7. How many blue balloons did Bob have at first?

Answer 1

Let B=# of blue balloons and G = # of green.

(B/G) = 4/5 means that B = 4G/5

Then (B-12)/(G-12) = 5/7

5G - 60 = 7B - 84

Now substitute

5G - 60 = 28G/5 - 84

25G - 300 = 28G - 420

3G = 120

You should be able to finish it from here.