Billy, Riordan and Cooper collected stamps in the ratio of 11 : 6 : 7. After Cooper gave ³₅ to Billy and Riordan, Cooper had 106 less stamps than Billy. The number of stamps that Riordan had increased by 30%. How many stamps did Billy and Cooper have in the end?

	Billy	Riordan	Cooper
Before	11 u	6 u	7 u
Change	+ 2.4 u	+ 1.8 u	- 4.2 u
After	13.4 u	7.8 u	2.8 u

Number of stamps that Cooper gave to Billy and Riordan
= ³₅ x 7 u
= 4.2 u

Number of stamps that Riordan received from Cooper
= ³⁰₁₀₀ x 6 u
= 1.8 u

Number of stamps that Billy received from Cooper
= 4.2 u - 1.8 u
= 2.4 u

Number of less stamps that Cooper had less than Billy
= 13.4 u - 2.8 u 
= 10.6 u

10.6 u = 106

1 u = 106 ÷ 10.6 = 10

Number of stamps that Billy and Cooper had
= 13.4 u + 2.8 u
= 16.2 u
= 16.2 x 10
= 162

Answer(s): 162