<PRE><B>Question 81376</B>
A hot tub is filled by two tanks. The first tank can fill the tub in 9 hours working alone, while the second tank (working alone) can fill it in 11 hours. If the two tanks work together, how long will it take them to fill the tub?
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Let t = time required when working together:
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Let the full tub = 1
:
{{{t/9}}} + {{{t/11}}} = 1
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Multiply equation by 9*11 = 99, to get rid of the denominators:
11t + 9t = 99
:
20t = 99
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t = 99/20
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t = 4.95 hrs or 4 + .95(60) = 4 hrs 57 min working together
:
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Check solution of t = 4.95:
{{{4.95/11}}} + {{{4.95/9}}} =
   .45 + .55 = 1</PRE>