26 March 2014
As per Para 7.1 of AS 11 average rate is the mean of the exchange rates in force during a period. Average rate could be for a week or a month. Since what is stated is the mean you should add up the exchange rate for each day of the month and divide by the number of days in the month. In case of holidays the same should ideally be excluded from the number of days since for the said date no rate would exist.