There were some green stamps and yellow stamps. The stamps were packed into 2 bags. At first, Packet X contained 300 stamps and 30% of them were yellow stamps. Packet Y contained 215 stamps and 80% of them were yellow stamps. How many green stamps and yellow stamps in total must be moved from Packet X to Packet Y such that 20% of the stamps in Packet X are green and 50% of the stamps in Packet Y are yellow?

	Packet X		Packet Y
Total	300		215
	Yellow stamps	Green stamps	Yellow stamps	Green stamps
Before	90	210	172	43
Change	- ?	- ?	+ ?	+ ?
After	4 u	1 u	1 p	1 p

Number of yellow stamps in Packet X at first
= 30% x 300
= ³⁰₁₀₀ x 300
= 90

Number of green stamps in Packet X at first
= 300 - 90
= 210

Number of yellow stamps in Packet Y at first
= 80% x 215
= ⁸⁰₁₀₀ x 215
= 172

Number of green stamps in Packet Y at first
= 215 - 172
= 43

Packet X in the end
20% = ²⁰₁₀₀ =¹₅
Yellow stamps : Green stamps = 4 : 1

Packet Y in the end
50% = ⁵⁰₁₀₀ =¹₂
Yellow stamps : Green stamps = 1 : 1

Total number of yellow stamps = 4 u + 1 p

4 u + 1 p = 90 + 172
4 u + 1 p = 262 

1 p = 262 - 4 u --- (1)

Total number of green stamps = 1 u + 1 p
1 u + 1 p = 210 + 43
1 u + 1 p = 253

1 p = 253 - 1 u --- (2)

(2) = (1)
253 - 1 u = 262 - 4 u
4 u - 1 u = 262 - 253
3 u = 9

1 u = 9 ÷ 3 = 3

Total number of green stamps and yellow stamps that must be moved from Packet X to Packet Y
= 300 - 5 u
= 300 - 5 x 3
= 300 - 15
= 285

Answer(s): 285