Prime Cost $= \text{Direct Materials} + \text{Direct Labour} + \text{Direct Expenses}$. It includes all costs that can be directly traced to a product unit — not just materials and labour. Option A is the most accurate because it captures all directly chargeable items. Option B is incomplete (it excludes direct expenses). Option C describes total production cost (including overheads). Option D is vague and incorrect.

The level of measurement (nominal, ordinal, interval, ratio) defines the nature of the relationship among values in a dataset — whether they can be ordered, whether differences are meaningful, and whether ratios make sense. This concept is fundamental in choosing appropriate statistical analyses.

Correct Answer: A — Level of measurement.

Apply the ideal gas law: $PV = n_{\text{total}}RT$

$n_{\text{total}} = 0.5 + x$

$200 \times 10 = (0.5 + x) \times R \times 1000$

$2000 = 1000R(0.5 + x)$

$2 = R(0.5 + x) = 0.5R + Rx$

$Rx = 2 - 0.5R$

$x = \dfrac{2 - 0.5R}{R} = \dfrac{4 - R}{2R}$

Magnetic susceptibility: $\chi = \frac{M}{H}$, where $M$ is magnetisation (magnetic moment per unit volume).

Volume of cube: $V = (1\times10^{-2})^3 = 10^{-6}\ \text{m}^3$

Magnetisation: $M = \frac{\text{dipole moment}}{V} = \frac{20\times10^{-6}}{10^{-6}} = 20\ \text{A/m}$

$\chi = \frac{M}{H} = \frac{20}{60\times10^3} = 3.33\times10^{-4}$

$\chi \approx 3.3 \times 10^{-4}$