Tina made buns for sale. 50% of the buns were chocolate buns and the rest were sardine and lotus paste buns in the ratio 4 : 1. If a customer bought 70% of the chocolate buns and all of the lotus paste buns, what percentage of the sardine buns must Tina sell for her to maintain the original percentage of chocolate buns at first? Leave your answer in decimals and correct to 1 decimal place.

Chocolate buns	Sardine buns	Lotus paste buns
1 u	1 u
	0.8 u	0.2 u

	Chocolate buns	Sardine buns	Lotus paste buns	Total buns
Before	1 u	0.8 u	0.2 u	2 u
Change	- 0.7 u	- 0.5 u	- 0.2 u
After	0.3 u	0.3 u	0	0.6 u

50% = ⁵⁰₁₀₀ = ¹₂
70% = ⁷⁰₁₀₀ = ⁷₁₀

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
= ⁴₅ x 1 u
= 0.8 u

Number of lotus paste buns at first
= 1 u - 0.8 u
= 0.2 u

Number of chocolate buns sold
= 70% x 1 u
= ⁷⁰₁₀₀ x 1 u
= ⁷₁₀ x 1 u
= 0.7 u

Number of lotus paste buns sold
= ¹₅ x 1 u
= 0.2 u

Number of chocolate buns left 
= 1 u - 0.7 u
= 0.3 u

To maintain the percentage of the chocolate buns in the end, 
50% → 0.3 u
100% → ^0.3₅₀ x 100 = 0.6 u

Total number of buns in the end to maintain the original percentage of chocolate buns = 0.6 u

Number of sardine buns left
= 0.6 u - 0.3 u
= 0.3 u

Number of sardine buns that Tina must sell to maintain the original percentage of chocolate buns
= 0.8 u - 0.3 u
= 0.5 u

Percentage of the sardine buns that Tina must sell
= ^0.5_0.8 x 100%
= 62.5%

Answer(s): 62.5%