What always comes into a house through the keyhole?

Can you find the mistake in the below statement?

Different lights make me strange by changing me into different sizes. What am I?

A boy and a girl are sitting on the porch.
"I'm a boy," says the child with black hair.
"I'm a girl," says the child with red hair.
If at least one of them is lying, who is which?

Manish and Manoj play 5 games of chess.
Both Manish and Manoj win the exact same number of games. There is no tie at all.

How?

Women do it once a year after they turn 19 but men get to do it only once in a lifetime. What is it?

Count the number of balls in picture below:

You need to move three matchsticks to form three squares. Can you do it?

I came first on earth but second on the heaven.
I also came twice in a week but found just once in a year.
I stay away from months but you can find me in February.

What am I?

A mathematics teacher took exams for his students. Out of the total students, 25% passed both the tests included in the exam. However, only 42% were able to clear the first test.

Can you find out the percentage of those students who passed the first test and also passed the second test?