Q. 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 π is the mean strength of the specimens and π is the standard deviation, the number of specimens (out of 20) with compressive strength less than π β 3π is

Ans: 0

Sol:

Mean strength,

β΄Β Number of specimen with compressive strength less than 15.485 MPa are zero.