Question 1118837
A vat of chocolate can be filled by an inlet pipe in 12 hours.
 An outlet pipe can empty the vat in 15 hours.
 How long will it take to fill the vat if both pipes are left open?
:
let t = time to fill the vat under these conditions
let the completed job = 1, (a full vat)
:
{{{t/12}}} - {{{t/15}}} = 1
get rid of the denominators, multiply equations by 60
60*{{{t/12}}} - 60*{{{t/15}}} = 60(1)
cancel denominators
5t - 4t = 60
t = 60 hrs to fill the vat