- A30
- B67.5
- C45
- D22.5
Step-by-Step Solution
Combined rate = 1/45 + 1/90 = 2/90 + 1/90 = 3/90 = 1/30 cistern per minute, so it fills in 30 minutes.
Answer: A) 30
A cistern on a terrace fills through one inlet in 45 minutes and through a second inlet in 90 minutes. With both inlets open, how many minutes does it take to fill?
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