What is common among 11, 69, and 88?

There’s a one-story house in which everything is yellow. Yellow walls, yellow doors, yellow furniture. What colour are the stairs?

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 ?

Chef Andrea has to light the kitchen stoves to open her restaurant for the day. There are three stoves in the kitchen: A glass stove, a brick stove, and a wood stove. She only has one match. Which does she light up first?

A B C D E F G H

These are the letters given to you. Now you have to find out the letter that comes two to the right of the letter which is immediately to the left of the letter that comes three to the right of the letter that comes midway between the letter two to the left of the letter C and the letter immediately to the right of the letter F.

A pond had 60 fish, out of which, all but 20 died.
How many fishes are now present in that pond?

How can you make number one disappear by adding something to it?

What occurs twice in a week, once in a year but never in a day?

Cristina was born in 1888. She just had her 30th birthday today how did that happen?

Take 9 from 6, 10 from 9, 50 from 40, and leave 6.

How Come ??