Correct option is A. 300
It is given that after $$4$$ days, out of $$28$$ days, the fort had enough food for $$1200$$ soldiers for $$(28-4=24)$$ days.
Let $$x$$ be the number of soldiers who left the fort.
Number of soldiers | $$1200$$ | $$1200-x$$ |
Number of days for which food lasts | $$24$$ | $$32$$ |
Since, the number of soldiers and the number of days for which the food lasts are in inverse variation, we have :$$\Rightarrow$$ $$1200\times 24=(1200-x)\times 32$$
$$\Rightarrow$$ $$\dfrac{1200\times 24}{32}=1200-x$$
$$\Rightarrow$$ $$900=1200-x$$
$$\Rightarrow$$ $$x=1200-900$$
$$\Rightarrow$$ $$x=300$$
$$\therefore$$ The soldiers which left the fort are $$300$$.