Step 1 :Let x be the number of apples at the beginning. After the first customer's purchase, the vendor had \(x - 3 - \frac{1}{4}x\) apples left. After the second customer's purchase, the vendor had 11 apples left. So, we can write the equation: \[11 = \left(x - 3 - \frac{1}{4}x\right) - \left(1 + \frac{1}{3}\left(x - 3 - \frac{1}{4}x\right)\right)\]
Step 2 :Solve the equation for x: \[x = 28\]
Step 3 :\boxed{\text{Final Answer: The fruit vendor had 28 apples for sale at the beginning of the day.}}