What is more useful when it is broken?

If "P" means "-", "Q" means "/", "R" means "+", and "S" means "*" then find the value of the following:

21 Q 7 R 9 S 10 P 13

Why do people go to bed?

You need to complete the maze by entering from the entrance marked below in the figure near the yellow circle, bottom left and leaving from the exit point near the green circle, bottom middle.

Rule of Game: You can move only by exchanging green and yellow circles.

I am weightless, but you can see me. Put me in a bucket, and I'll make it lighter. 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?

Two batsman each on 94 runs. Seven runs needed to win in last 3 balls. Both make 100*. How?

If you toss a coin 10 times and it lands heads up every time, what are the chances it will land heads up if you toss it again?

You enter your friend's room. He is not in his room. Although you see that on the bed there are two dogs, five cats, two giraffes and three pigs. Also, a couple of chickens and ducks are flying in the room.

Calculate the number of legs standing on the floor.

The more of this there is, the less you see. What is it?