The frequency distribution of the compressive strength of 20 concrete cube specimens is given in the table.
If $\mu$ is the mean strength of the specimens and $\sigma$ is the standard deviation, the number of specimens (out of 20 ) with compressive strength less than $\mu-3 \sigma$ is
The frequency distribution of the compressive strength of 20 concrete cube specimens is given in the table.
If $\mu$ is the mean strength of the specimens and $\sigma$ is the standard deviation, the number of specimens (out of 20 ) with compressive strength less than $\mu-3 \sigma$ is