A company observes the lifespan of 560 lightbulbs and finds that their data follows a normal distribution. what is the approximate number of light bulbs that fall within two standard deviations from the mean?

Empirical rule can be used to estimate the number of values that lie with 1, 2 or 3 standard deviations of a Normally distributed population.

According to the empirical rule, 95% of the values lie within 2 standard deviations of the mean.

Total number of bulbs = n = 560

95% of n = 0.95 x 560 = 532

This means, 532 bulbs will lie within 2 standard deviations from the mean