A fresh water tap fills a fish tank in 40 minutes. The same tank is filled by a salt water tap in 120 minutes. If both the taps are open, how many minutes will it take to fill the tank?
Given:
Fresh tap fills in 40 min; salt tap fills in 120 min. Both open together.
Formula:
Combined rate = rate1 + rate2.
Time = 1 / (combined rate).
Solution:
Rate of fresh tap = 1/40 tank per minute.
Rate of salt tap = 1/120 tank per minute.
Combined rate = 1/40 + 1/120 = (3 + 1)/120 = 4/120 = 1/30 tank per minute.
Time to fill = 1 / (1/30) = 30 minutes.
Correct Answer: (b) 30 minutes
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