Upon any distribution of New South Wales into electoral districts, the boundaries of each proposed electoral district shall be so determined that, at the time the distribution is made, the number of persons entitled to vote at a general election of Members of the Legislative Assembly in each proposed electoral district is equal to the quotient obtained by dividing the number of persons entitled at that time to vote at any such general election in all of the proposed electoral districts by the number of those proposed electoral districts, but subject to a margin of allowance not exceeding 10 per cent more or less of that quotient.