If it took eight men ten hours to build a wall, how long would it take four men to build it?

Two men play a dice game involving roll of two standard dice. Man X says that a 12 will be rolled first. Man Y says that two consecutive 7s will be rolled first. The men keep rolling until one of them wins.

What is the probability that X will win ?

If,
29 - 1 = 30
9 - 1 = 10
14 - 1 = 15

Based on similar logic, Can you prove that the below algebraic equation is true?
11 - 1 = 10 ?

The Federal bank of London is abducted by the robbers. The head of the robbers asked the cashier to empty their money vault to them and when suddenly cashier got a call from her father. To avoid any suspicion, the robber asked the cashier to pick the call and reply her father in the shortest manner possible.

The cashier told her father "Is there an emergency father, Call me when you are free and I will help you in your furnishing" and then the cashier hung up the phone.

After 10 minutes, police arrived at the crime scene.

How did the police know about the robbery?

What is so fragile that saying its name breaks it?

There are people and strange monkeys on this island, and you can not tell who is who (Edit: until you understand what they said - see below). They speak either only the truth or only lies.
Who are the following two guys?
A: B is a lying monkey. I am human.
B: A is telling the truth.

A farmer went to a market and bought a wolf, a goat, and a cabbage. On his way home, the farmer came to the bank of a river and rented a boat. But crossing the river by boat, the farmer could carry only himself and a single one of his purchases: the wolf, the goat, or the cabbage. If left unattended together, the wolf would eat the goat, or the goat would eat the cabbage. The farmer’s challenge was to carry himself and his purchases to the far bank of the river, leaving each purchase intact. How did he do it?

A boy was at a carnival and went to a booth where a man said to the boy, "If I write your exact weight on this piece of paper then you have to give me $50, but if I cannot, I will pay you $50." The boy looked around and saw no scale so he agrees, thinking no matter what the carny writes he'll just say he weighs more or less. In the end the boy ended up paying the man $50. How did the man win the bet?

How can you write nineteen in a manner that if we take out one, it becomes twenty?

A father told his three sons he would die soon and he needed to decide which one of them to give his property to. He said, “Go to the market and buy something large enough to fill my bedroom, but small enough to fit in your pocket. From this, I will decide which of you is the wisest and worthy enough to inherit my land.” They all went to the market, and each came back with a different item. The father told his sons to come into his bedroom one at a time and try to fill up his bedroom with their items. The first son came in and put some pieces of cloth he bought and laid them across the room, but it barely covered the floor. The second son came in and laid some hay on the floor, but there was only enough to cover half the floor. The third son came in and showed his father what he bought. He wound up getting the property. What did the third son show his father?