If there are fifteen crows on a fence and the farmer shoots a third of them, how many crows are left?

Can you find the mistake in the below statement?

What is the relationship between these matchstick pictures below?

What am I?

There is a square piece of paper with a hole that is denoted by the circle on the top right side in the given picture. You have to cut the paper in a manner that it forms two and only two separate pieces of paper and then rearrange the pieces in a manner that the holes come in the centre of the paper.

I have one of the three numbers: 1, 2, or 3 in my mind. I speak only truth. You can ask me just one question for which I will only reply in yes or no or don't know. What question will you ask from me so that you are able to know the number?

Take 9 from 6, 10 from 9, 50 from 40, and leave 6.

How Come ??

Two natural numbers have a sum of less than 100 and are greater than one.

John knows the product of the numbers and Jacob knows the sum of numbers.

The following conversation takes place between them:
John: 'I am not aware of those numbers.'
Jacob: 'I knew you wouldn't be. I am not aware myself.'
John: 'Now I know them!'
Jacob: 'Now I know them, too!'

What are the two numbers?

Until it is measured, not known. Yet how you miss it when it has gone. What is it?

In 1990, a person is 15 years old. In 1995, that same person is 10 years old. How can this be?