Mary made buns for sale. 50% of the buns were curry buns and the rest were sardine and lotus paste buns in the ratio 3 : 1. If a customer bought 75% of the curry buns and all of the lotus paste buns, what percentage of the sardine buns must Mary sell for her to maintain the original percentage of curry buns at first? Leave your answer in decimals and correct to 1 decimal place.

Curry buns	Sardine buns	Lotus paste buns
1 u	1 u
	0.75 u	0.25 u

	Curry buns	Sardine buns	Lotus paste buns	Total buns
Before	1 u	0.75 u	0.25 u	2 u
Change	- 0.75 u	- 0.5 u	- 0.25 u
After	0.25 u	0.25 u	0	0.5 u

50% = ⁵⁰₁₀₀ = ¹₂
75% = ⁷⁵₁₀₀ = ³₄

Total number of buns = 2 u

Number of sardine and lotus paste buns
= 2 u - 1 u
= 1 u

Number of sardine buns at first
= ³₄ x 1 u
= 0.75 u

Number of lotus paste buns at first
= 1 u - 0.75 u
= 0.25 u

Number of curry buns sold
= 75% x 1 u
= ⁷⁵₁₀₀ x 1 u
= ³₄ x 1 u
= 0.75 u

Number of lotus paste buns sold
= ¹₄ x 1 u
= 0.25 u

Number of curry buns left 
= 1 u - 0.75 u
= 0.25 u

To maintain the percentage of the curry buns in the end, 
50% → 0.25 u
100% → ^0.25₅₀ x 100 = 0.5 u

Total number of buns in the end to maintain the original percentage of curry buns = 0.5 u

Number of sardine buns left
= 0.5 u - 0.25 u
= 0.25 u

Number of sardine buns that Mary must sell to maintain the original percentage of curry buns
= 0.75 u - 0.25 u
= 0.5 u

Percentage of the sardine buns that Mary must sell
= ^0.5_0.75 x 100%
= 66.7%

Answer(s): 66.7%