The answer is 96 min, here is why:
x / 240 + x / 160 = 1
<span>2x + 3x = 480 </span>
<span>5x = 480 </span>
<span>x = 96 min
(</span><span>Drainage rate of first pipe = 480000/240 = 2000 l/min </span>
<span>Drainage rate of second tube = 480000/160 = 3000 l/min </span>
<span>Combined drainage rate = 5000 l/min </span>
<span>Time to drain = 480000/5000 = 96 min. )</span>
A polyhedron is a 3D solid with many faces
