self Maths Puzzle

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?

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self Other Question

You have a balance scale with four weights. With these four weights you must balance any whole number load (in ounces) from 1 all the way up to 40.

How much should each of the four weights weigh?

(You may place weights on both sides of the scale at the same time.)
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?