1. **Problem statement:** We want to estimate the number of runners in the London Marathon on 25th April 2010 whose birthday was on that exact day. 2. **Understanding the problem:** There were 37,527 runners in total. We assume birthdays are uniformly distributed across the 365 days of the year (ignoring leap years). 3. **Formula used:** The expected number of runners with a birthday on a specific day is given by: $$\text{Expected number} = \text{Total runners} \times \frac{1}{365}$$ 4. **Calculation:** $$37,527 \times \frac{1}{365} = \frac{37,527}{365}$$ 5. **Perform division:** $$\frac{37,527}{365} \approx 102.8$$ 6. **Interpretation:** Since the number of runners must be whole, we estimate about 103 runners had their birthday on 25th April 2010. **Final answer:** Approximately **103** runners had their birthday on that day.