Mary made buns for sale. 60% of the buns were kaya buns and the rest were lotus paste and mushroom buns in the ratio 3 : 1. If a customer bought 75% of the kaya buns and all of the mushroom buns, what percentage of the lotus paste buns must Mary sell for her to maintain the original percentage of kaya buns at first? Leave your answer in decimals and correct to 1 decimal place.

Kaya buns	Lotus paste buns	Mushroom buns
3 u	2 u
	1.5 u	0.5 u

	Kaya buns	Lotus paste buns	Mushroom buns	Total buns
Before	3 u	1.5 u	0.5 u	5 u
Change	- 2.25 u	- 1 u	- 0.5 u
After	0.75 u	0.5 u	0	1.25 u

60% = ⁶⁰₁₀₀ = ³₅
75% = ⁷⁵₁₀₀ = ³₄

Total number of buns = 5 u

Number of lotus paste and mushroom buns
= 5 u - 3 u
= 2 u

Number of lotus paste buns at first
= ³₄ x 2 u
= 1.5 u

Number of mushroom buns at first
= 2 u - 1.5 u
= 0.5 u

Number of kaya buns sold
= 75% x 3 u
= ⁷⁵₁₀₀ x 3 u
= ³₄ x 3 u
= 2.25 u

Number of mushroom buns sold
= ¹₄ x 2 u
= 0.5 u

Number of kaya buns left 
= 3 u - 2.25 u
= 0.75 u

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

Total number of buns in the end to maintain the original percentage of kaya buns = 1.25 u

Number of lotus paste buns left
= 1.25 u - 0.75 u
= 0.5 u

Number of lotus paste buns that Mary must sell to maintain the original percentage of kaya buns
= 1.5 u - 0.5 u
= 1 u

Percentage of the lotus paste buns that Mary must sell
= ¹_1.5 x 100%
= 66.7%

Answer(s): 66.7%