While designing a concrete mix, if 5% of the results are allowed to fall below the characteristic strength and if the assumed standard deviation is 6 MPa, then what will be the Target mean strength (TMS) (MPa) of M40 grade of concrete?

Correct option is C

​$$\text{Target mean strength is given by} \\f_m = f_{ck} + 1.65 \delta \\\text{Where } f_m = \text{Target mean strength} \\f_{ck} = \text{Characteristic strength} \\\delta = \text{Standard deviation} \\f_m = 40 + 1.65 \times 6 \\= 49.9 \, \text{MPa} \\\approx 50 \, \text{MPa}$$​​