The desired characteristic strength of a mix is 20 N/mm2. The standard deviation is 4 N/mm2 for 150 mm size of concrete cubes; and K = 1.645. The average strength of the cubes will be nearly
1
38.2 N/mm2
2
32.4 N/mm2
3
26.6 N/mm2
4
22.8 N/mm2
The desired characteristic strength of a mix is 20 N/mm2. The standard deviation is 4 N/mm2 for 150 mm size of concrete cubes; and K = 1.645. The average strength of the cubes will be nearly