If eleven plus two equals one, what does nine plus five equal?

Can you replace the X (both small and big x) with the numbers between 1 to 19 such that all the rows of 3 numbers between X (big x) sum to 23?

I am a type of vehicle that has two wheels and is powered by humans. What am I?
Hint 1: You can ride me for exercise.
Hint 2: I am environment-friendly.

In a town, there are four houses located at different distances from each other. Following are the distances:

The third house is 60 meters apart from the first house.
The fourth house is 40 meters apart from the second house.
The third house is 10 meters nearer to the fourth house than it is to the second house.

Can you find out the distance between the fourth and the first house?

What is the largest amount of money that you can possess in change and still if someone asks you for a dollar, you won't be able to give?

A shepherd had 18 sheep, out of which, all but ten died.

Can you tell us how many sheep was he left with?

Find the hidden tiger in the given optical illusion ?

What building has the most stories?

You may enter, but you may not come in. I have space, but no room. I have keys, but open no lock. What am I?

What work can one never finish?