self Maths Puzzle

A pool has four taps.

The first tap takes two days to fill the pool, the second tap three days, the third four days and the last one only 6 hours.

How long will it take to fill the pool using all 4 taps at once?

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self Other Question

You intend to fly non-stop around the world.

But you can only go halfway around the world on a full tank.

However you can arrange many planes exactly like yours to assist with refuelling.

Assuming refuelling can be done midair, ignoring refuelling and turning time, and without crashing any plane, what is the minimum number of planes you will need?
We have two red, two green and two yellow balls.

For each color, one ball is heavy and the other is light.

All heavy balls weigh the same. All light balls weigh the same.

How many weighings on a beam balance are necessary to identify the three heavy balls?