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 ?

13 decks of cards have been mixed. What is the minimum number of cards that must be taken out from the above-mixed cards to guarantee at least one 'four of a kind?

What is the end of everything?

I am taken from a mine and shut up in a wooden case, from which I am never released, and yet I am used by almost every person. What am I?

Bopanna was working on a murder case when he received a message about the location of the murder weapon.
The message was encrypted as below.

"deb mitciv eht edisni neddih si nopaew redrum ehT"

Tell me the location of the murder weapon.

On her drawing table, Sayna lit 12 coloured candles. A few seconds later she blew two candles off.

How many candles Sayna have at the end?

A man and his wife were doing missionary work near the city of Nairobi in the country of Kenya in eastern Africa. Their housing had not yet been completed, so the man, the woman, and their six year old daughter were spending a few nights in the jungle in three small pup tents. During their third night there, the woman was awakened by the call of a hyena passing by, so she got out of her tent to see if her young daughter had been frightened by the noise. As she peered into her daughter's tent she was surprised to see the dark figures of lion, a panther, and a cheetah which were curled up next to her daughter. Seeing her daughter was asleep and unharmed, the woman slowly and quietly withdrew from the tent, and simply returned to her own tent and went back to bed. How could this child's mother leave her daughter in such a dangerous situation, and simply ignore what she had just witnessed without intervening in some way? How can such emotional coldness ever be explained; or is there something here we are missing?

What is the word or phrase?

What are the five permanent members of the UN Security Council?

a) France, Germany, Italy, Japan, United Kingdom
b) Canada, Mexico, Saudi Arabia, Turkey, United Arab Emirates
c) Brazil, India, Nigeria, South Africa, South Korea
d) China, France, Russia, United Kingdom, United States

Bea Smith, Vera Bennett, Franky Doyle and Doreen Anderson were in Wentworth Prison for murder. But their behaviour in the jails is appreciated by the warden and the warden decided to give all these 4 prisoners 11 cupcakes. They all like cupcakes and they had all cupcakes in no matter of time but they do not know how many cupcakes each individual had. Therefore Bea started the conversation Bea: "Hey T-Vera, did you have more cupcakes than I had ?"Vera: "I do not know girl, Hey Franky, did you have more cupcakes than I had ?".Franky: "I do not know"Doreen replied instantly: "I know how exactly how many cupcakes each of you had?" So can you tell how many cupcakes each of them had?