1. The desired quality of concrete is being obtained on site by control testing using 150mm cubes prepared from samples of the concrete used on site. Typical test results are given below; Cube 1 2 3 4 5 7 10 11 12 Number Estimated 37.0 42.0 41.5 30.0 42.0 41.0 47.5 29 40.5 31 38.5 42.5 28days strength fC Cube 13 14 15 16 17 18 19 20 21 22 23 24 25 Number Estimated 34.0 42 34 31.5 36 34 33 37 37.5 32.5 30.0 41.0 27.0 28days strength If the characteristics strength, fcu = 30.0].1 mm'z, design standard deviation, 5 =5.0u mm'l; design mean strength, fcu =38.0u mm'2 and design mean range = 5.5u mm'z. [s adequate control being exercised