Computation of goodwill

As per my knowledge,

If the capital employed in the beginning of the year is not given,average capital can be ascertained by deducting half of the profits of the year from the capital employed at the end of the year

No there is no specific reason behind this logic it is simply when we have to caluclate Average figure then we should at leat two figure or more. Hence there is same logic when there is no opening value is given then we can provide the 1/2 of the curent so it can get average automatically.