There were brown, yellow and purple balls in a box. Sean put another 5 brown balls and 9 purple balls in the box, then the ratio of the number of yellow balls to the number of purple balls became 5 : 2. Then, he doubled the number of brown balls and removed 29 purple balls. The ratio of the number of brown balls to yellow balls became 2 : 1. He counted and found that there were a total of 124 balls left in the box. Find the number of brown balls that he had in the end.

	Brown balls	Yellow balls	Purple balls	Total
Before	5 u - 5	5 u	2 u - 9
Change 1	+ 5		+ 9
After 1	1x5 = 5 u	5 u	2 u
Change 2	+ 1x5 = 5 u		- 29
After 2	2x5 = 10 u	1x5 = 5 u	2 u - 29	124

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

Total number of balls in the end
= 10 u + 5 u + 2 u - 29
= 17 u - 29

17 u - 29 = 124
17 u = 124 + 29
17 u = 153

1 u = 153 ÷ 17 = 9

Number of brown balls in the end
= 10 u 
= 10 x 9
= 90

Answer(s): 90