Question

The number of nails of a given length is normally distributed with a mean length of 5.00 in. and a standard deviation of 0.03 in. Find the number of nails in a bag of 120 that are between 4.97 and 5.03 in. Long.

Answer 1

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

$P(4.97<X<5.03)\approx0.68$

So out of 120 nails, we can expect $0.68\cdot120=81.6\approx82$ nails to be within the prescribed length.

Answer 2

The number of nails in a bag of 120 that are between 4.97 and 5.03 in. Long will be 82.

What is a normal distribution?

A normal distribution is a symmetrical continuous probability distribution in which values are usually clustered around the mean.

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

P(4.97<X<5.03)068

So out of 120 nails, we can expect  0.68 x120= 81.57=82 nails to be within the prescribed length.

Hence the number of nails in a bag of 120 that are between 4.97 and 5.03 in. Long will be 82.

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