Esther made sandwiches for sale. 40% of the sandwiches were chocolate sandwiches and the rest were curry and lotus paste sandwiches in the ratio 4 : 1. If a customer bought 85% of the chocolate sandwiches and all of the lotus paste sandwiches, what percentage of the curry sandwiches must Esther sell for her to maintain the original percentage of chocolate sandwiches at first? Leave your answer in decimals and correct to 1 decimal place.

Chocolate sandwiches	Curry sandwiches	Lotus paste sandwiches
2 u	3 u
	2.4 u	0.6 u

	Chocolate sandwiches	Curry sandwiches	Lotus paste sandwiches	Total sandwiches
Before	2 u	2.4 u	0.6 u	5 u
Change	- 1.7 u	- 1.95 u	- 0.6 u
After	0.3 u	0.45 u	0	0.75 u

40% = ⁴⁰₁₀₀ = ²₅
85% = ⁸⁵₁₀₀ = ¹⁷₂₀

Total number of sandwiches = 5 u

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

Number of curry sandwiches at first
= ⁴₅ x 3 u
= 2.4 u

Number of lotus paste sandwiches at first
= 3 u - 2.4 u
= 0.6 u

Number of chocolate sandwiches sold
= 85% x 2 u
= ⁸⁵₁₀₀ x 2 u
= ¹⁷₂₀ x 2 u
= 1.7 u

Number of lotus paste sandwiches sold
= ¹₅ x 3 u
= 0.6 u

Number of chocolate sandwiches left 
= 2 u - 1.7 u
= 0.3 u

To maintain the percentage of the chocolate sandwiches in the end, 
40% → 0.3 u
100% → ^0.3₄₀ x 100 = 0.75 u

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

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

Number of curry sandwiches that Esther must sell to maintain the original percentage of chocolate sandwiches
= 2.4 u - 0.45 u
= 1.95 u

Percentage of the curry sandwiches that Esther must sell
= ^1.95_2.4 x 100%
= 81.3%

Answer(s): 81.3%