What is the Surname of Barbie Doll?

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

Can you count the number of squares in the figure below?

What's the only room from which no one can enter or leave

What will be the best approach to finding all the prime numbers less than 75 that leave an odd reminder when we divide them with 5?

A man lives on the fifteenth floor of an apartment building. Every morning he takes the elevator down to the lobby and leaves the building. In the evening, he gets into the elevator, and, if there is someone else in the elevator, or if it was raining that day, he goes back to his floor directly. Otherwise, he goes to the tenth floor and walks up five flights of stairs to his apartment. Can you explain why he does this?

Jim and Sarah are in a long-distance relationship. Jim buys an engagement ring for Sarah and wants to mail it to her. Unfortunately, the only way to ensure the ring will be received is to place a lock on the package. Jim has locks and Sarah has locks, but neither has keys for each other’s locks. How can they make sure the ring isn’t stolen?

The more it dries, the wetter it becomes. Can you tell what it is?

You have a roll of cloth 1km long. You have a machine which cuts this roll into pieces of 10-meter-long cloth.

How long would it take for the machine to cut the roll if each cut took 4 secs?

What is full of holes but still holds water?