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

Egg buns	Mushroom buns	Sardine buns
2 u	3 u
	2 u	1 u

	Egg buns	Mushroom buns	Sardine 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 mushroom and sardine buns
= 5 u - 2 u
= 3 u

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

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

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

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

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

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

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

Number of mushroom buns that Wendy must sell to maintain the original percentage of egg buns
= 2 u - 0.75 u
= 1.25 u

Percentage of the mushroom buns that Wendy must sell
= ^1.25₂ x 100%
= 62.5%

Answer(s): 62.5%