There were some green stamps and silver stamps. The stamps were packed into 2 bags. At first, Bag R contained 90 stamps and 40% of them were silver stamps. Bag S contained 50 stamps and 80% of them were silver stamps. How many green stamps and silver stamps in total must be moved from Bag R to Bag S such that 20% of the stamps in Bag R are green and 50% of the stamps in Bag S are silver?

	Bag R		Bag S
Total	90		50
	Silver stamps	Green stamps	Silver stamps	Green stamps
Before	36	54	40	10
Change	- ?	- ?	+ ?	+ ?
After	4 u	1 u	1 p	1 p

Number of silver stamps in Bag R at first
= 40% x 90
= ⁴⁰₁₀₀ x 90
= 36

Number of green stamps in Bag R at first
= 90 - 36
= 54

Number of silver stamps in Bag S at first
= 80% x 50
= ⁸⁰₁₀₀ x 50
= 40

Number of green stamps in Bag S at first
= 50 - 40
= 10

Bag R in the end
20% = ²⁰₁₀₀ =¹₅
Silver stamps : Green stamps = 4 : 1

Bag S in the end
50% = ⁵⁰₁₀₀ =¹₂
Silver stamps : Green stamps = 1 : 1

Total number of silver stamps = 4 u + 1 p

4 u + 1 p = 36 + 40
4 u + 1 p = 76 

1 p = 76 - 4 u --- (1)

Total number of green stamps = 1 u + 1 p
1 u + 1 p = 54 + 10
1 u + 1 p = 64

1 p = 64 - 1 u --- (2)

(2) = (1)
64 - 1 u = 76 - 4 u
4 u - 1 u = 76 - 64
3 u = 12

1 u = 12 ÷ 3 = 4

Total number of green stamps and silver stamps that must be moved from Bag R to Bag S
= 90 - 5 u
= 90 - 5 x 4
= 90 - 20
= 70

Answer(s): 70