For 100 sq. m cement concrete (1 : 2 : 4) 4 cm thick floor, the quantity of cement required, is

Volume of cement concrete is =0.04*100=4cum
10%extra for unevenness and loss =4.4cum
Loose volume =50%extra =4.4*1.5=6.6cum
Volume of cement =6.6/(1+2+4)=0.942cum

Totel volume = 7, thickness of floor = 4
Stp1. 1÷7 = 0.1428
Stp2. 2÷7 = 0.2857
Stp3. 4÷7 = 0.5714
All values are multiple and × 4
=0.1428×0.2857×0.5714×4
=0.09324
Assume = 0.094
Ans = 0.94m^3

Generally to calculate the Cement, fine aggregate and coarse aggregate the following method will be followed,

Wet Qty. of concrete = 100 Sqm * 0.04m thickness = 4.00 Cum
To get the dry volume of concrete, generally wet volume of concrete will be multiplied by 150%.

Therefore 4.00 Cum * 150% = 6.00 Cum.

Cement Qty. = Dry volume of concrete / ( Sum of the ratio values).

= 6.00 /( 1+2+4).
= 0.857 Cum of Cement i.e.25 No. of bags.

But here they considered 164.5% instead of 150%.

Dry volume of concrete = 4 * 164.5% = 6.58 Cum.

Cement Qty. = 6.58/ (1+2+4) = 0.94 Cum