A histogram shows test scores for 500 students with a distribution that is approximately normal. The mean is $\mu = 75$ and the standard deviation is $\sigma = 10$. If we define a bin width of $w = 5$, what is the approximate height (frequency) of the bin representing scores in the interval $[70, 75)$ using the normal probability density function $f(x) = \frac{1}{\sigma \sqrt{2\pi}} e^{-\frac{1}{2}(\frac{x-\mu}{\sigma})^2}$?