4.97 is 1 standard deviation below the mean, since 5.00 - 0.03 = 4.97. Similarly, 5.03 is 1 standard deviation above the mean. The 68-95-99.7 rule (sometimes called "empirical rule") says that approximately 68% of any normally distributed population lies within 1 standard deviation of the mean, so
So out of 120 nails, we can expect nails to be within the prescribed length.
About 3 nails is correct on grad point
Thus the number of nails that are less than 4.94 will be: