Tiffany made sandwiches for sale. 55% of the sandwiches were kaya sandwiches and the rest were beef and sardine sandwiches in the ratio 4 : 1. If a customer bought 75% of the kaya sandwiches and all of the sardine sandwiches, what percentage of the beef sandwiches must Tiffany sell for her to maintain the original percentage of kaya sandwiches at first? Leave your answer in decimals and correct to 1 decimal place.

Kaya sandwiches	Beef sandwiches	Sardine sandwiches
11 u	9 u
	7.2 u	1.8 u

	Kaya sandwiches	Beef sandwiches	Sardine sandwiches	Total sandwiches
Before	11 u	7.2 u	1.8 u	20 u
Change	- 8.25 u	- 4.95 u	- 1.8 u
After	2.75 u	2.25 u	0	5 u

55% = ⁵⁵₁₀₀ = ¹¹₂₀
75% = ⁷⁵₁₀₀ = ³₄

Total number of sandwiches = 20 u

Number of beef and sardine sandwiches
= 20 u - 11 u
= 9 u

Number of beef sandwiches at first
= ⁴₅ x 9 u
= 7.2 u

Number of sardine sandwiches at first
= 9 u - 7.2 u
= 1.8 u

Number of kaya sandwiches sold
= 75% x 11 u
= ⁷⁵₁₀₀ x 11 u
= ³₄ x 11 u
= 8.25 u

Number of sardine sandwiches sold
= ¹₅ x 9 u
= 1.8 u

Number of kaya sandwiches left 
= 11 u - 8.25 u
= 2.75 u

To maintain the percentage of the kaya sandwiches in the end, 
55% → 2.75 u
100% → ^2.75₅₅ x 100 = 5 u

Total number of sandwiches in the end to maintain the original percentage of kaya sandwiches = 5 u

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

Number of beef sandwiches that Tiffany must sell to maintain the original percentage of kaya sandwiches
= 7.2 u - 2.25 u
= 4.95 u

Percentage of the beef sandwiches that Tiffany must sell
= ^4.95_7.2 x 100%
= 68.8%

Answer(s): 68.8%