Opal made buns for sale. 40% of the buns were chicken buns and the rest were kaya and chocolate buns in the ratio 4 : 1. If a customer bought 75% of the chicken buns and all of the chocolate buns, what percentage of the kaya buns must Opal sell for her to maintain the original percentage of chicken buns at first? Leave your answer in decimals and correct to 1 decimal place.

Chicken buns	Kaya buns	Chocolate buns
2 u	3 u
	2.4 u	0.6 u

	Chicken buns	Kaya buns	Chocolate buns	Total buns
Before	2 u	2.4 u	0.6 u	5 u
Change	- 1.5 u	- 1.65 u	- 0.6 u
After	0.5 u	0.75 u	0	1.25 u

40% = ⁴⁰₁₀₀ = ²₅
75% = ⁷⁵₁₀₀ = ³₄

Total number of buns = 5 u

Number of kaya and chocolate buns
= 5 u - 2 u
= 3 u

Number of kaya buns at first
= ⁴₅ x 3 u
= 2.4 u

Number of chocolate buns at first
= 3 u - 2.4 u
= 0.6 u

Number of chicken buns sold
= 75% x 2 u
= ⁷⁵₁₀₀ x 2 u
= ³₄ x 2 u
= 1.5 u

Number of chocolate buns sold
= ¹₅ x 3 u
= 0.6 u

Number of chicken buns left 
= 2 u - 1.5 u
= 0.5 u

To maintain the percentage of the chicken buns in the end, 
40% → 0.5 u
100% → ^0.5₄₀ x 100 = 1.25 u

Total number of buns in the end to maintain the original percentage of chicken buns = 1.25 u

Number of kaya buns left
= 1.25 u - 0.5 u
= 0.75 u

Number of kaya buns that Opal must sell to maintain the original percentage of chicken buns
= 2.4 u - 0.75 u
= 1.65 u

Percentage of the kaya buns that Opal must sell
= ^1.65_2.4 x 100%
= 68.8%

Answer(s): 68.8%