1: A barrel of water weighs 60 pounds. What must you put in it for it to weigh 40 pounds?

2: There are 20 people in an empty, square room. Each person has full sight of the entire room and everyone in it without turning his head or body, or moving in any way (other than the eyes). Where can you place an apple so that all but one person can see it?

3: How do you make the number 7 even without addition, subtraction, multiplication or division?

4: How can you drop an egg on a concrete floor without cracking it?

1. Since the barrel of water weighs 60 pounds, in order for the barrel of water to weigh 40 pounds, then one has to put holes into them. This will help reduce the weight.

2. Since the 20 people in the room has full sight of the entire room and can see everyone in it without turning their head or body, then the apple should be put on the head of someone. In this case, 19 people will be able to see it but the person having the apple on the head can't see it.

3. To make the number 7 even without the addition, subtraction, multiplication or division of numbers, then one has to remove S from the Seven. Removing S from Seven becomes EVEN.

4. The question here relates to the concrete floor. In this case, concrete floors are usually hard, tough and durable. Therefore, the egg can't crack the floor. Therefore, one should just drop it.

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