What is black when you buy it, red when you use it, and gray when you throw it away?

If I remove one from eleven it becomes Ten and if I remove one from nine also becomes Ten. How?

Begin with a word, five letters to my name,
Remove the first and last but I am the same
Take out my middle and still, I remain.
What word am I?

I am a five-letter word and people eat me. If you remove the first letter I become an energy form. If you remove the first two letters, I am needed to live. Scramble the last three letters and I am a drink. What word am I?

If you drop me I’m sure to crack, but give me a smile and I’ll always smile back. What am I?

Christina, Allison and Lena are 3 daughters of John a well-known Mathematician, When I asked John the age of their daughters. He replied "The current age of her daughters is prime. Also, the difference between their ages is also prime."

How old are the daughters?

What has to be broken before you can use it?

What number comes next in the series?

5 15 5 18 5 24 14 20 _

Why are all black people so quick ?

You need to move three matchsticks to form three squares. Can you do it?