The frequency distribution of the compressive strength of 20 concrete cube specimens is given in the table.
f(MPa) Number of specimens with
compressive strength equal to f
23 4
28 2
22.5 5
31 5
29 4
If
μ is the mean strength of the specimens and
σ is the standard deviation the number of specimens (out of 20) with compressive strength less than
μ−3σ is ________.
- 0