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.
The widths，w cm ，of a random sample of 150 leaves of a certain kind were measured．The sample mean of w was found to be 3.12 cm ．
Using this sample，an approximate 95 % confidence interval for the population mean of the widths in centimetres was found to be［3．01，3．23］．
Calculate an estimate of the population standard deviation．
3.12+z×150σ=3.23
OE - correct expression. Any z, but must be a z value.
z=1.96
σ=0.687 (3sf) [cm]