Find The Next Number In The Sequence

30 10 15 13 0 16 -15 ?

what does the below math rebus puzzle mean?

Can you place six matchsticks in a manner that each of the matchsticks is in touch with the other five matchsticks?

John needs to purchase 100 chocolates from three different shops and he has exactly 100 rupees to do that which he must spend entirely. He must buy at least 1 Chocolate from each shop.

The first shop is selling each chocolate at 5 paise, the second is selling at 1 rupee and the third is selling at 5 rupees.

How many chocolates should he buy from each shop?

The more it dries, the wetter it becomes. Can you tell what it is?

What is a word made up of 4 letters, yet is also made up of 3. Sometimes is written with 9 letters, and then with 4. Rarely consists of 6, and never is written with 5.

What is in seasons, seconds, centuries and minutes but not in decades, years or days?

I am a three digit number.
My tens digit is five more than my ones digit.
My hundreds digit is eight less than my tens digit.
What number am I?

A network of 20 x 10 squares is given to you.

Can you calculate how many unique squares and rectangles can be formed combining two or more individual squares ?

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