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# Z-test

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A new company is manufacturing light bulbs. The CEO claims that the average light bulb lasts 260 days. A researcher selects 25 bulbs for testing. The sample bulbs last an average of 250 days with a standard deviation of 20 days. If the CEO's claim was true, can we conclude that 25 random bulbs will last 260 days at a 0.01 level of significance?

Can you explain the steps in getting the answer?

##### Solution Summary

This solution lays out the steps in hypothesis testing for a z test.

##### Solution Preview

This is a hypothesis testing question that uses a z test.

I'm going to walk you through the steps of hypothesis testing.

1. State your null and alternative hypotheses.
Null: average lightbulb lasts 260 days
Alternative: average lightbulb does not last 260 days

2. We're going to use a z-test that ...

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