Use only one mathematical symbol and all numbers (0-9) to get a sum of 99

A new Engineering building containing 100 offices had just been completed. John was hired to paint the numbers 1 to 100 on the doors. How many times will John have to paint the number nine (9)?

Pronounced as one letter,
And written with three,
Two letters there are,
And two only in me.
I am double, I am single,
I am black blue and grey,
I am read from both ends,
And the same either way.

A word I know,
Six letters contain,
Subtract just one,
And twelve is what remains.

How can you make a TV, a bed, a dog, and a car liquid?

Chocolate costs 6 rupees and a Toy costs 5 rupees. If you have 32 rupees in total, how many chocolates and how many Toys can be purchased with that amount?

In the image given, you can find several triangles. Can you count them all?

What always comes into a house through the keyhole?

A boy and a girl are sitting on the porch.
"I'm a boy," says the child with black hair.
"I'm a girl," says the child with red hair.
If at least one of them is lying, who is which?

Below the four parts have been reorganised. The four partitions are exactly the same in both arrangements. Why is there a hole?