1. **State the problem:** Given the coefficient of variation (CV) is 87.5% and the mean ($\mu$) is 4, find the standard deviation ($\sigma$). 2. **Formula used:** The coefficient of variation is defined as $$\text{CV} = \frac{\sigma}{\mu} \times 100\%$$ where $\sigma$ is the standard deviation and $\mu$ is the mean. 3. **Rearrange the formula to find $\sigma$:** $$\sigma = \frac{\text{CV} \times \mu}{100}$$ 4. **Substitute the given values:** $$\sigma = \frac{87.5 \times 4}{100}$$ 5. **Calculate:** $$\sigma = \frac{350}{100} = 3.5$$ 6. **Answer:** The standard deviation is $3.5$. This means the data varies on average by 3.5 units from the mean of 4.