Barbara made croissants for sale. 45% of the croissants were sardine croissants and the rest were beef and mushroom croissants in the ratio 3 : 1. If a customer bought 75% of the sardine croissants and all of the mushroom croissants, what percentage of the beef croissants must Barbara sell for her to maintain the original percentage of sardine croissants at first? Leave your answer in decimals and correct to 1 decimal place.

Sardine croissants	Beef croissants	Mushroom croissants
9 u	11 u
	8.25 u	2.75 u

	Sardine croissants	Beef croissants	Mushroom croissants	Total croissants
Before	9 u	8.25 u	2.75 u	20 u
Change	- 6.75 u	- 5.5 u	- 2.75 u
After	2.25 u	2.75 u	0	5 u

45% = ⁴⁵₁₀₀ = ⁹₂₀
75% = ⁷⁵₁₀₀ = ³₄

Total number of croissants = 20 u

Number of beef and mushroom croissants
= 20 u - 9 u
= 11 u

Number of beef croissants at first
= ³₄ x 11 u
= 8.25 u

Number of mushroom croissants at first
= 11 u - 8.25 u
= 2.75 u

Number of sardine croissants sold
= 75% x 9 u
= ⁷⁵₁₀₀ x 9 u
= ³₄ x 9 u
= 6.75 u

Number of mushroom croissants sold
= ¹₄ x 11 u
= 2.75 u

Number of sardine croissants left 
= 9 u - 6.75 u
= 2.25 u

To maintain the percentage of the sardine croissants in the end, 
45% → 2.25 u
100% → ^2.25₄₅ x 100 = 5 u

Total number of croissants in the end to maintain the original percentage of sardine croissants = 5 u

Number of beef croissants left
= 5 u - 2.25 u
= 2.75 u

Number of beef croissants that Barbara must sell to maintain the original percentage of sardine croissants
= 8.25 u - 2.75 u
= 5.5 u

Percentage of the beef croissants that Barbara must sell
= ^5.5_8.25 x 100%
= 66.7%

Answer(s): 66.7%