To compare the diameter of a grain of salt to the width of a human hair, we need to divide the diameter of the grain of salt by the width of the human hair.
Given:
- Diameter of a grain of salt = \(3 \times 10^{-4}\) meters
- Width of a human hair = \(8 \times 10^{-5}\) meters
Now, we can calculate the ratio:
\[ \text{Ratio} = \frac{\text{Diameter of grain of salt}}{\text{Width of human hair}} = \frac{3 \times 10^{-4}}{8 \times 10^{-5}} \]
To simplify this, we can calculate it as follows:
\[ \frac{3}{8} \times \frac{10^{-4}}{10^{-5}} = \frac{3}{8} \times 10^{1} = \frac{3}{8} \times 10 = \frac{30}{8} = 3.75 \]
Thus, the diameter of a grain of salt is about 3.75 times longer than the width of a human hair.