Question

III) The municipality of New York supplies 2 million cubic metres of water per month to the city of New York. If a household consumes about 30killo-littres of water per month, estimate the number of residents in New York ,assuming that a household has five members on everage.

Answer 1

Let N = no. of residents
N/5 = number of households
1 cubic meter = 10^6 cubic cm = 1000 liters = 1 kiloliter
Monthly consumption = (N/5)*30 kiloliter
= 2*10^6 kiloliter
This results in N = 1/3 million.
That is too low. I question the figures you provided.

According to
http://www.nytimes.com/2006/10/03/nyregion/03water.html?_r=1
New York City's daily consumption is 1.1 billion gallons, which would make the monthly consumption 33 billion gallons or 8.5 billion liters or 8.5 million kiloliters, not 2 million.