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 ๐ is the mean strength of the specimens and ๐ is the standard deviation, the number of specimens (out of 20) with compressive strength less than ๐ โ 3๐ is
Ans: 0
Sol:
Mean strength,
โดย Number of specimen with compressive strength less than 15.485 MPa are zero.
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