Question

A body weighs $W_{1}$ in air, and $W_{2}$ in water. What is its relative density?

Answer 1

Relative Density= $\frac{Weight of body in air}{Loss of weight in water}$
Hence, R.D=$\frac{W1}{W1-W2}$  

Answer 2

Relative density is the ratio of density of a material to density of water. If A body weighs W₁ in air and W₂ in water, its relative density is given by

$R.D= \frac{W_1}{W_1-W_2}$

Derivation:
Density of water = w
density of body = p
volume of body = v
W₁ = pvg
W₂ = (p-w)vg

$RD= \frac{p}{w}= \frac{pvg}{wvg} = \frac{pvg}{pvg-pvg+wvg} = \frac{pvg}{pvg-(pvg-wvg)} = \frac{W1}{W1-W2}$