Hazel made buns for sale. 40% of the buns were kaya buns and the rest were mushroom and chicken buns in the ratio 3 : 1. If a customer bought 80% of the kaya buns and all of the chicken buns, what percentage of the mushroom buns must Hazel 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	Mushroom buns	Chicken buns
2 u	3 u
	2.25 u	0.75 u

	Kaya buns	Mushroom buns	Chicken buns	Total buns
Before	2 u	2.25 u	0.75 u	5 u
Change	- 1.6 u	- 1.65 u	- 0.75 u
After	0.4 u	0.6 u	0	1 u

40% = ⁴⁰₁₀₀ = ²₅
80% = ⁸⁰₁₀₀ = ⁴₅

Total number of buns = 5 u

Number of mushroom and chicken buns
= 5 u - 2 u
= 3 u

Number of mushroom buns at first
= ³₄ x 3 u
= 2.25 u

Number of chicken buns at first
= 3 u - 2.25 u
= 0.75 u

Number of kaya buns sold
= 80% x 2 u
= ⁸⁰₁₀₀ x 2 u
= ⁴₅ x 2 u
= 1.6 u

Number of chicken buns sold
= ¹₄ x 3 u
= 0.75 u

Number of kaya buns left 
= 2 u - 1.6 u
= 0.4 u

To maintain the percentage of the kaya buns in the end, 
40% → 0.4 u
100% → ^0.4₄₀ x 100 = 1 u

Total number of buns in the end to maintain the original percentage of kaya buns = 1 u

Number of mushroom buns left
= 1 u - 0.4 u
= 0.6 u

Number of mushroom buns that Hazel must sell to maintain the original percentage of kaya buns
= 2.25 u - 0.6 u
= 1.65 u

Percentage of the mushroom buns that Hazel must sell
= ^1.65_2.25 x 100%
= 73.3%

Answer(s): 73.3%