To find out how many cards Alang sold, we need to calculate 4% of the total number of cards sold, which is 250.
First, we convert the percentage to a decimal: \[ 4% = \frac{4}{100} = 0.04 \]
Next, we calculate the number of cards sold by Alang: \[ \text{Cards sold by Alang} = 250 \times 0.04 \]
Now performing the multiplication: \[ 250 \times 0.04 = 10 \]
Therefore, Alang sold \(\boxed{10}\) cards.