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

I have two coins.
* One of the coins is a faulty coin having a tail on both sides of it.
* The other coin is a perfect coin (heads on side and tail on other).

I blindfold myself and pick a coin and put the coin on the table. The face of the coin towards the sky is the tail.

What is the probability that another side is also tail?

Replace the question mark with the correct number in below Picture:

A girl has as many brothers as sisters, but each brother has only half as many brothers as sisters. How many brothers and sisters are there in the family?

If 21x = 79x, what is the value of x?

Our product and our sum always give the same answer. Who are we?

Replace each alphabet with the number (1-9) to make the below equation correct.

AB * C = DE - F = GH / I

Three friends decide to distribute the soda cans they had among them. When all of them had drunk four cans each, the total number of cans that remained was equal to the cans each one of them had after they had divided the cans.

Can you calculate the total number of cans before distribution?

John was running from 40 thieves. John has got 3 gold boxes which weigh as 4kg, 2kg, and 1kg respectively. A witty man asked John to stay with him for seven days in exchange for 1kg gold per day. John needs to stay there for seven days and also do not want to give the witty man any advance. How can John pay for his seven days stay?

There is a square of a particular number which when doubled, becomes 7 more than its quarter.

Can you find the number?