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

Kaya croissants	Mushroom croissants	Sardine croissants
1 u	1 u
	0.75 u	0.25 u

	Kaya croissants	Mushroom croissants	Sardine croissants	Total croissants
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 croissants = 2 u

Number of mushroom and sardine croissants
= 2 u - 1 u
= 1 u

Number of mushroom croissants at first
= ³₄ x 1 u
= 0.75 u

Number of sardine croissants at first
= 1 u - 0.75 u
= 0.25 u

Number of kaya croissants sold
= 75% x 1 u
= ⁷⁵₁₀₀ x 1 u
= ³₄ x 1 u
= 0.75 u

Number of sardine croissants sold
= ¹₄ x 1 u
= 0.25 u

Number of kaya croissants left 
= 1 u - 0.75 u
= 0.25 u

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

Total number of croissants in the end to maintain the original percentage of kaya croissants = 0.5 u

Number of mushroom croissants left
= 0.5 u - 0.25 u
= 0.25 u

Number of mushroom croissants that Dana must sell to maintain the original percentage of kaya croissants
= 0.75 u - 0.25 u
= 0.5 u

Percentage of the mushroom croissants that Dana must sell
= ^0.5_0.75 x 100%
= 66.7%

Answer(s): 66.7%