Natalie made sandwiches for sale. 60% of the sandwiches were mushroom sandwiches and the rest were beef and curry sandwiches in the ratio 4 : 1. If a customer bought 75% of the mushroom sandwiches and all of the curry sandwiches, what percentage of the beef sandwiches must Natalie sell for her to maintain the original percentage of mushroom sandwiches at first? Leave your answer in decimals and correct to 1 decimal place.

Mushroom sandwiches	Beef sandwiches	Curry sandwiches
3 u	2 u
	1.6 u	0.4 u

	Mushroom sandwiches	Beef sandwiches	Curry sandwiches	Total sandwiches
Before	3 u	1.6 u	0.4 u	5 u
Change	- 2.25 u	- 1.1 u	- 0.4 u
After	0.75 u	0.5 u	0	1.25 u

60% = ⁶⁰₁₀₀ = ³₅
75% = ⁷⁵₁₀₀ = ³₄

Total number of sandwiches = 5 u

Number of beef and curry sandwiches
= 5 u - 3 u
= 2 u

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

Number of curry sandwiches at first
= 2 u - 1.6 u
= 0.4 u

Number of mushroom sandwiches sold
= 75% x 3 u
= ⁷⁵₁₀₀ x 3 u
= ³₄ x 3 u
= 2.25 u

Number of curry sandwiches sold
= ¹₅ x 2 u
= 0.4 u

Number of mushroom sandwiches left 
= 3 u - 2.25 u
= 0.75 u

To maintain the percentage of the mushroom sandwiches in the end, 
60% → 0.75 u
100% → ^0.75₆₀ x 100 = 1.25 u

Total number of sandwiches in the end to maintain the original percentage of mushroom sandwiches = 1.25 u

Number of beef sandwiches left
= 1.25 u - 0.75 u
= 0.5 u

Number of beef sandwiches that Natalie must sell to maintain the original percentage of mushroom sandwiches
= 1.6 u - 0.5 u
= 1.1 u

Percentage of the beef sandwiches that Natalie must sell
= ^1.1_1.6 x 100%
= 68.8%

Answer(s): 68.8%