At the end of November, Gwen had four times as many 20-cent coins as 50-cent coins in her piggy bank. She took out 90 20-cent coins and exchanged it for 50-cent coins of the same value. In December, she saved another 26 20-cent coins and some 50-cent coins. She then had four times as many 50-cent coins in the end. She had 500 coins in the end. How many 50-cent coins did she save in December?

	20-cent	50-cent	Total
Before	4 u	1 u
Change 1	- 90	+ 36
Change 2	+ 26	+ ?
After	1 p	4 p	500

Total number of coins in the end
= 1 p + 4 p 
= 5 p

5 p = 500

1 p = 500 ÷ 5 = 100

Number of 20-cent in the end
= 1 p
= 100

Number of 20-cent at first
= 100 - 26 + 90
= 164

4 u = 164

1 u = 164 ÷ 4 = 41

Number of 50-cent coins in the end
= 4 p
= 4 x 100
= 400

Total value of 90 20-cent coins 
= 90 x 20
= 1800¢

Number of 50-cent coins that was exchanged from 90 20-cent coins 
= 1800 ÷ 50
= 36

Number of 50-cent coins that Gwen saved in December
= 4 p - 1 u - 36
= 400 - 41 - 36 
= 323 

Answer(s): 323