Xuan had some blue pens and yellow pens in 2 bags. In Bag A, the ratio of the number of blue pens to yellow pens was 9 : 4. In Bag B, the number of blue pens was 3 times the number of yellow pens. Xuan transferred ³₄ of the yellow pens from Bag A to Bag B. The number of pens in Bag A became 150 and the ratio of the number of blue pens to yellow pens in Bag B became 6 : 7.

1. How many yellow pens were transferred from Bag A to Bag B?
2. What was the number of pens in Bag B after the transfer?

	Bag A		Bag B
	Blue	Yellow	Blue	Yellow
Comparing blue pens and yellow pens at first	9 u	4 u	3x2 = 6 p	1x2 = 2 p
Before		4 u
Change		- 3 u		+ 3 u
After		1 u
Comparing blue pens and yellow pens in the end	9 u	1 u	6 p	7 p

(a)
Total number of pens in the end for Bag A
= 9 u + 1 u
= 10 u

10 u = 150

1 u = 150 ÷ 10 = 15

Number of yellow pens that were transferred from Bag A to Bag B
= 3 u
= 3 x 15
= 45

(b)
The number of blue pens in Bag B remains unchanged.  Make the number of blue pens in Bag B the same.  LCM of 3 and 6 is 6. 

Increase in the number of yellow pens in Bag B
= 7 p - 2 p
= 5 p

5 p = 3 u
5 p = 45

1 p = 45 ÷ 5 = 9

Number of pens in Bag B in the end
= 6 p + 7 p
= 13 p
= 13 x 9
= 117

Answer(s): (a) 45; (b) 117