Question 230986
One pump can drain a pool in 11 minutes.
 When a second pump is also used, the pool only takes 6 minutes to drain.
 How long would it take the second pump to drain the pool if it were the only pump in use?
;
Let t = time required by the 2nd pump alone
:
Let the completed job = 1 (a drained pool)
:
{{{6/11}}} + {{{6/t}}} = 1
multiply by 11t, results:
6t + 6(11) = 11t
:
66 = 11t - 6t
:
66 = 5t
t = {{{66/5}}}
t = 13.2 min, the 2nd pipe alone
;
:
Check on  a calc: enter (6/11) + (6/13.2) = 1