To calculate the retention rate, you can use the formula:
\[ \text{Retention Rate} = \left( \frac{\text{Number of Customers Retained}}{\text{Total Number of Customers Last Year}} \right) \times 100 \]
In this case:
- Number of Customers Retained = 400
- Total Number of Customers Last Year = 600
Now plug in the values:
\[ \text{Retention Rate} = \left( \frac{400}{600} \right) \times 100 = \left( \frac{2}{3} \right) \times 100 \approx 66.67% \]
When rounded, this gives us approximately 67%.
So the correct answer is 67%.