Olivia bought a total of 240 big and small chocolate bars. Then she decided to exchange 20% of her big chocolate bars for the small ones in the ratio of 1 : 5. After the exchange, she had 288 chocolate bars. What percentage of the chocolate bars she bought were small ones?

	Big chocolate bars	Small chocolate bars	Total
Before	5 u	?	240
Change	- 1 u
Comparing big and small chocolate bars at exchange	- 1 u	+ 5 u	+ 48
After	4 u	?	288

20% = ²⁰₁₀₀ = ¹₅

The number of big chocolate bars that were exchanged for small chocolate bars was repeated.  

Number of extra chocolate bars that Olivia received due to the exchange
= 5 u - 1 u
= 4 u

4 u = 288 - 240
4 u = 48

1 u = 48 ÷ 4 = 12

Number of small chocolate bars at first
= 240 - 5 u
= 240 - 5 x 12
= 240 - 60
= 180

Percentage of the chocolate bars Olivia bought that were small ones
=  ¹⁸⁰₂₄₀ x 100%
= 75% 

Answer(s): 75%