If the stability of the production during 1990 to 1995 is defined as,

$$\frac{\text{Average Production}}{ \text{Maximum Production}\ -\text{Minimum Production}}$$

then, which product is most stable?

Stability of Product P = $$\frac{\left(45+25+40+35+75+55\right)}{\left(75-25\right)\times\ 6}=0.91$$

Stability of Product Q = $$\frac{\left(99+40+108+60+40+70\right)}{\left(108-40\right)\times\ 6}=1.02$$

Stability of Product R = $$\frac{\left(72+91+107+62+131+120\right)}{\left(131-62\right)\times\ 6}=1.408$$

Stability of Product S = $$\frac{\left(115+159+165+140+88+98\right)}{\left(165-88\right)\times\ 6}=1.65$$

Thus, the correct option is D.