Practise constructing and interpreting confidence intervals for a population mean using a known variance or large sample, an appropriate z-value and the standard error.
Batteries of type A are known to have a mean life of 150 hours. It is required to test whether a new type of battery, type B, has a shorter mean life than type A batteries.
Calculate a 94% confidence interval for the population mean life of type B batteries.
147 +/- z x 15120
Expression of correct form must be a z value
z=1.881 [or 1.882]
144 to 150 (3 s.f.)
Must be an interval
Incorrect z value can only score M1B0A0