# Probability: Working with the standard distribution curve.

A company installs 5000 light bulbs, each with an average life of 500 hours and a standard deviation of 100 hours, and a distribution approximated by a normal curve. Find the percentage of bulbs that can be expected to last the period of time between 540 hours and 780 hours? Less than 690 hours?

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#### Solution Preview

1) Here we take Sd=100 as the population Sd, which is already known.

We are to solve Pr(540<X<780)=Pr(X<780)- ...

#### Solution Summary

The standard distribution curve is used to calculate probabilities.

$2.19