Mrs Yong had some red apples and green apples. 60% of the apples were red apples and the rest were green apples. There were 192 more red apples than green apples. After Mrs Yong sold some red apples, the percentage of red apples she had left became 25%. How many red apples did Mrs Yong sell? Answer: ___

1. Find the percentage difference between red and green apples initially.

Percentage of green apples initially = $100\% - 60\% = 40\%$
Difference in percentage = $60\% - 40\% = 20\%$

2. Calculate the initial number of red and green apples.

$20\%$ of total apples $\rightarrow 192$
$1\%$ of total apples $\rightarrow 192 \div 20 = 9.6$
Initial red apples = $60 \times 9.6 = 576$
Initial green apples = $40 \times 9.6 = 384$

3. Use the unchanged quantity (green apples) to find the new number of red apples.

The number of green apples remains unchanged at $384$.
New percentage of green apples = $100\% - 25\% = 75\%$
$75\%$ of new total $\rightarrow 384$
New percentage of red apples is $25\%$, which is $\frac{1}{3}$ of $75\%$.
New red apples = $384 \div 3 = 128$

4. Calculate the number of red apples sold.

Red apples sold = Initial red apples $-$ New red apples
$= 576 - 128 = 448$