Jack, Sean and Christopher collected stamps in the ratio of 7 : 5 : 10. After Christopher gave ¹₅ to Jack and Sean, Christopher had -5 less stamps than Jack. The number of stamps that Sean had increased by 30%. How many stamps did Jack and Christopher have in the end?

	Jack	Sean	Christopher
Before	7 u	5 u	10 u
Change	+ 0.5 u	+ 1.5 u	- 2 u
After	7.5 u	6.5 u	8 u

Number of stamps that Christopher gave to Jack and Sean
= ¹₅ x 10 u
= 2 u

Number of stamps that Sean received from Christopher
= ³⁰₁₀₀ x 5 u
= 1.5 u

Number of stamps that Jack received from Christopher
= 2 u - 1.5 u
= 0.5 u

Number of less stamps that Christopher had less than Jack
= 7.5 u - 8 u 
= -0.5 u

-0.5 u = -5

1 u = -5 ÷ -0.5 = 10

Number of stamps that Jack and Christopher had
= 7.5 u + 8 u
= 15.5 u
= 15.5 x 10
= 155

Answer(s): 155