Find The Next Number In The Sequence

30 10 15 13 0 16 -15 ?

In the image below, can you find the value of an angle(y)

I possess a head

I flaunt a tail

But I don't have mouth or legs

Can you find out who I am?

Why is a river so rich ?

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 ?

I come in different shapes and sizes.
Parts of me are curved, other parts are straight.
You can put me anywhere you like,
but there is only one right place for me.
What am I?

In a science lab, a petri dish hosts a healthy colony of yeast for an experiment. Now every minute, all the yeast cells divide into two. At noon, there was just a single cell of yeast and at 1:22, the Petri dish was half full. Can you calculate when the dish will be full of yeast?

A Shopkeeper collects 71 rupees in the form of 20 paisa and 25 paisa.
He collects a total of 324 coins.

Can you tell me how many number of 20-paisa and 25-paisa he got?

Can you find the hidden animal in the picture below?

The square root of number 121 is "11". What is the square root of the number "12345678987654321."?