There were pink, gold and black balls in a bottle. Sean put another 7 pink balls and 9 black balls in the bottle, then the ratio of the number of gold balls to the number of black balls became 5 : 2. Then, he doubled the number of pink balls and removed 21 black balls. The ratio of the number of pink balls to gold balls became 2 : 1. He counted and found that there were a total of 98 balls left in the bottle. Find the number of pink balls that he had in the end.

	Pink balls	Gold balls	Black balls	Total
Before	5 u - 7	5 u	2 u - 9
Change 1	+ 7		+ 9
After 1	1x5 = 5 u	5 u	2 u
Change 2	+ 1x5 = 5 u		- 21
After 2	2x5 = 10 u	1x5 = 5 u	2 u - 21	98

The number of gold balls remains unchanged. Make the number of gold balls the same. LCM of 1 and 5 is 5.

Total number of balls in the end
= 10 u + 5 u + 2 u - 21
= 17 u - 21

17 u - 21 = 98
17 u = 98 + 21
17 u = 119

1 u = 119 ÷ 17 = 7

Number of pink balls in the end
= 10 u 
= 10 x 7
= 70

Answer(s): 70