Billy, Ahmad and Cooper collected stickers in the ratio of 12 : 6 : 5. After Cooper gave ⁷₁₀ to Billy and Ahmad, Cooper had 670 less stickers than Billy. The number of stickers that Ahmad had increased by 10%. How many stickers did Billy and Cooper have in the end?

	Billy	Ahmad	Cooper
Before	12 u	6 u	5 u
Change	+ 2.9 u	+ 0.6 u	- 3.5 u
After	14.9 u	6.6 u	1.5 u

Number of stickers that Cooper gave to Billy and Ahmad
= ⁷₁₀ x 5 u
= 3.5 u

Number of stickers that Ahmad received from Cooper
= ¹⁰₁₀₀ x 6 u
= 0.6 u

Number of stickers that Billy received from Cooper
= 3.5 u - 0.6 u
= 2.9 u

Number of less stickers that Cooper had less than Billy
= 14.9 u - 1.5 u 
= 13.4 u

13.4 u = 670

1 u = 670 ÷ 13.4 = 50

Number of stickers that Billy and Cooper had
= 14.9 u + 1.5 u
= 16.4 u
= 16.4 x 50
= 820

Answer(s): 820