Question 987171
.
The volume of the tank is 30*40*50 = 60,000 {{{cm^3}}}.


The volume of the water is {{{1/2}}}.60000 = 30000 {{{cm^3}}}. 


The time to empty the reservoir is {{{30000/12}}} = 2500 minutes = {{{41}}}{{{2/3}}} hours = 41 hours 40 minutes.