Rachel made muffins for sale. 40% of the muffins were chocolate muffins and the rest were sardine and chicken muffins in the ratio 4 : 1. If a customer bought 70% of the chocolate muffins and all of the chicken muffins, what percentage of the sardine muffins must Rachel sell for her to maintain the original percentage of chocolate muffins at first? Leave your answer in decimals and correct to 1 decimal place.

Chocolate muffins	Sardine muffins	Chicken muffins
2 u	3 u
	2.4 u	0.6 u

	Chocolate muffins	Sardine muffins	Chicken muffins	Total muffins
Before	2 u	2.4 u	0.6 u	5 u
Change	- 1.4 u	- 1.5 u	- 0.6 u
After	0.6 u	0.9 u	0	1.5 u

40% = ⁴⁰₁₀₀ = ²₅
70% = ⁷⁰₁₀₀ = ⁷₁₀

Total number of muffins = 5 u

Number of sardine and chicken muffins
= 5 u - 2 u
= 3 u

Number of sardine muffins at first
= ⁴₅ x 3 u
= 2.4 u

Number of chicken muffins at first
= 3 u - 2.4 u
= 0.6 u

Number of chocolate muffins sold
= 70% x 2 u
= ⁷⁰₁₀₀ x 2 u
= ⁷₁₀ x 2 u
= 1.4 u

Number of chicken muffins sold
= ¹₅ x 3 u
= 0.6 u

Number of chocolate muffins left 
= 2 u - 1.4 u
= 0.6 u

To maintain the percentage of the chocolate muffins in the end, 
40% → 0.6 u
100% → ^0.6₄₀ x 100 = 1.5 u

Total number of muffins in the end to maintain the original percentage of chocolate muffins = 1.5 u

Number of sardine muffins left
= 1.5 u - 0.6 u
= 0.9 u

Number of sardine muffins that Rachel must sell to maintain the original percentage of chocolate muffins
= 2.4 u - 0.9 u
= 1.5 u

Percentage of the sardine muffins that Rachel must sell
= ^1.5_2.4 x 100%
= 62.5%

Answer(s): 62.5%