Jade made sandwiches for sale. 50% of the sandwiches were sardine sandwiches and the rest were mushroom and chocolate sandwiches in the ratio 4 : 1. If a customer bought 70% of the sardine sandwiches and all of the chocolate sandwiches, what percentage of the mushroom sandwiches must Jade sell for her to maintain the original percentage of sardine sandwiches at first? Leave your answer in decimals and correct to 1 decimal place.

Sardine sandwiches	Mushroom sandwiches	Chocolate sandwiches
1 u	1 u
	0.8 u	0.2 u

	Sardine sandwiches	Mushroom sandwiches	Chocolate sandwiches	Total sandwiches
Before	1 u	0.8 u	0.2 u	2 u
Change	- 0.7 u	- 0.5 u	- 0.2 u
After	0.3 u	0.3 u	0	0.6 u

50% = ⁵⁰₁₀₀ = ¹₂
70% = ⁷⁰₁₀₀ = ⁷₁₀

Total number of sandwiches = 2 u

Number of mushroom and chocolate sandwiches
= 2 u - 1 u
= 1 u

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

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

Number of sardine sandwiches sold
= 70% x 1 u
= ⁷⁰₁₀₀ x 1 u
= ⁷₁₀ x 1 u
= 0.7 u

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

Number of sardine sandwiches left 
= 1 u - 0.7 u
= 0.3 u

To maintain the percentage of the sardine sandwiches in the end, 
50% → 0.3 u
100% → ^0.3₅₀ x 100 = 0.6 u

Total number of sandwiches in the end to maintain the original percentage of sardine sandwiches = 0.6 u

Number of mushroom sandwiches left
= 0.6 u - 0.3 u
= 0.3 u

Number of mushroom sandwiches that Jade must sell to maintain the original percentage of sardine sandwiches
= 0.8 u - 0.3 u
= 0.5 u

Percentage of the mushroom sandwiches that Jade must sell
= ^0.5_0.8 x 100%
= 62.5%

Answer(s): 62.5%