Tina made sandwiches for sale. 50% of the sandwiches were lotus paste sandwiches and the rest were beef and curry sandwiches in the ratio 4 : 1. If a customer bought 75% of the lotus paste sandwiches and all of the curry sandwiches, what percentage of the beef sandwiches must Tina sell for her to maintain the original percentage of lotus paste sandwiches at first? Leave your answer in decimals and correct to 1 decimal place.

Lotus paste sandwiches	Beef sandwiches	Curry sandwiches
1 u	1 u
	0.8 u	0.2 u

	Lotus paste sandwiches	Beef sandwiches	Curry sandwiches	Total sandwiches
Before	1 u	0.8 u	0.2 u	2 u
Change	- 0.75 u	- 0.55 u	- 0.2 u
After	0.25 u	0.25 u	0	0.5 u

50% = ⁵⁰₁₀₀ = ¹₂
75% = ⁷⁵₁₀₀ = ³₄

Total number of sandwiches = 2 u

Number of beef and curry sandwiches
= 2 u - 1 u
= 1 u

Number of beef sandwiches at first
= ⁴₅ x 1 u
= 0.8 u

Number of curry sandwiches at first
= 1 u - 0.8 u
= 0.2 u

Number of lotus paste sandwiches sold
= 75% x 1 u
= ⁷⁵₁₀₀ x 1 u
= ³₄ x 1 u
= 0.75 u

Number of curry sandwiches sold
= ¹₅ x 1 u
= 0.2 u

Number of lotus paste sandwiches left 
= 1 u - 0.75 u
= 0.25 u

To maintain the percentage of the lotus paste sandwiches in the end, 
50% → 0.25 u
100% → ^0.25₅₀ x 100 = 0.5 u

Total number of sandwiches in the end to maintain the original percentage of lotus paste sandwiches = 0.5 u

Number of beef sandwiches left
= 0.5 u - 0.25 u
= 0.25 u

Number of beef sandwiches that Tina must sell to maintain the original percentage of lotus paste sandwiches
= 0.8 u - 0.25 u
= 0.55 u

Percentage of the beef sandwiches that Tina must sell
= ^0.55_0.8 x 100%
= 68.8%

Answer(s): 68.8%