People make me, save me, change me, raise me. What am I?

What is the four-digit number in which the first digit is one-third the second, the third is the sum of the first two, and the last is three times the second?

In a fruit store, there was a unique weighing machine that was made to weigh only cherries and strawberries as they were priced the same.

Other fruits like watermelons or mango had different machines as they were expensive.

A man successfully buys watermelons at the price of cherries. How?

What number do you get when you multiply all of the numbers on a telephone's number pad?

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?

Prove that twice of ten is the same as twice of eleven.

What is always in front of you but can’t be seen?

I am a type of room you cannot enter or leave. Raised from the ground below, I could be poisonous or a delicious treat. What am I?

Irene killed hundreds of people mercilessly and yet the police were not able to put her behind the bars. Why?

You’re out on the water and see a boat filled with people. You look away for a second and look back again, but this time you don’t see a single person on the boat. Why? Hint: The boat did not sink.