Anonymous

# Clearly stating hypotheses, test the engineers claim at the 5% significance level...?

A pump's lifetime D follows a normal distribution with mean of 1500 hours and variance also 1500 hours. A plumping station needs 5 working pumps, without which it fails.

After 1500 hours the pumps are still all working. The engineers believe the lifetime is at least 1500 hours.A sample of 5 pumps are tested and have a mean lifetime of 1550 hours.Clearly stating hypotheses, test the engineers claim at the 5% significance level.So, we use X~N(μ, σ) right?Therefore, I get X~N(1500, sqrt(1500)) P(X > 1550) right?But the answer booklet has the answer as :X~N(1500, (1500/5)) ???

### 1 Answer

Relevance

- fcas80Lv 72 months ago
Are you testing whether one pump is > 1550, or whether the mean of five pumps is > 1550? If the latter, then var of the mean = 1500/5

Still have questions? Get answers by asking now.