Tina made sandwiches for sale. 60% of the sandwiches were beef sandwiches and the rest were egg and lotus paste sandwiches in the ratio 4 : 1. If a customer bought 85% of the beef sandwiches and all of the lotus paste sandwiches, what percentage of the egg sandwiches must Tina sell for her to maintain the original percentage of beef sandwiches at first? Leave your answer in decimals and correct to 1 decimal place.

Beef sandwiches	Egg sandwiches	Lotus paste sandwiches
3 u	2 u
	1.6 u	0.4 u

	Beef sandwiches	Egg sandwiches	Lotus paste sandwiches	Total sandwiches
Before	3 u	1.6 u	0.4 u	5 u
Change	- 2.55 u	- 1.3 u	- 0.4 u
After	0.45 u	0.3 u	0	0.75 u

60% = ⁶⁰₁₀₀ = ³₅
85% = ⁸⁵₁₀₀ = ¹⁷₂₀

Total number of sandwiches = 5 u

Number of egg and lotus paste sandwiches
= 5 u - 3 u
= 2 u

Number of egg sandwiches at first
= ⁴₅ x 2 u
= 1.6 u

Number of lotus paste sandwiches at first
= 2 u - 1.6 u
= 0.4 u

Number of beef sandwiches sold
= 85% x 3 u
= ⁸⁵₁₀₀ x 3 u
= ¹⁷₂₀ x 3 u
= 2.55 u

Number of lotus paste sandwiches sold
= ¹₅ x 2 u
= 0.4 u

Number of beef sandwiches left 
= 3 u - 2.55 u
= 0.45 u

To maintain the percentage of the beef sandwiches in the end, 
60% → 0.45 u
100% → ^0.45₆₀ x 100 = 0.75 u

Total number of sandwiches in the end to maintain the original percentage of beef sandwiches = 0.75 u

Number of egg sandwiches left
= 0.75 u - 0.45 u
= 0.3 u

Number of egg sandwiches that Tina must sell to maintain the original percentage of beef sandwiches
= 1.6 u - 0.3 u
= 1.3 u

Percentage of the egg sandwiches that Tina must sell
= ^1.3_1.6 x 100%
= 81.3%

Answer(s): 81.3%