Rachel made buns for sale. 40% of the buns were kaya buns and the rest were chocolate and egg buns in the ratio 2 : 1. If a customer bought 75% of the kaya buns and all of the egg buns, what percentage of the chocolate buns must Rachel sell for her to maintain the original percentage of kaya buns at first? Leave your answer in decimals and correct to 1 decimal place.

Kaya buns	Chocolate buns	Egg buns
2 u	3 u
	2 u	1 u

	Kaya buns	Chocolate buns	Egg buns	Total buns
Before	2 u	2 u	1 u	5 u
Change	- 1.5 u	- 1.25 u	- 1 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 chocolate and egg buns
= 5 u - 2 u
= 3 u

Number of chocolate buns at first
= ²₃ x 3 u
= 2 u

Number of egg buns at first
= 3 u - 2 u
= 1 u

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

Number of egg buns sold
= ¹₃ x 3 u
= 1 u

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

To maintain the percentage of the kaya 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 kaya buns = 1.25 u

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

Number of chocolate buns that Rachel must sell to maintain the original percentage of kaya buns
= 2 u - 0.75 u
= 1.25 u

Percentage of the chocolate buns that Rachel must sell
= ^1.25₂ x 100%
= 62.5%

Answer(s): 62.5%