Question

The quality control manager at a compact fluorescent light bulb (CFL) factory needs to determine whether the mean life of a larger shipment of CFL is equal to 7,500 hours.

The population standard deviation is 1,200 hours.

A random sample of 64 CFLs indicates a sample mean life of 7,250 hours.

At the 0.05 level of significance, is there evidence that the mean life is different from 7,500 hours?

Answer 1

H0: =7500

Ha: 7500

Sample size, n =64

Sample mean, =7250

Population standard deviation, = 1200

Standard error of ​​​​​​, SE(​​​​​​) = =1200//8 =120

Test statistc, Z= (​​​​​​) /

= (7250-7500)/120 =-25/12= -2.083

At

Zcrit= 1.96

|Z| =2.083>1.96

So,reject null hypothesis. There is enough evidence to conclude that Mean life is different from 7500 hours.

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