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

Place a mathematical symbol between the numerals 5 and 9 in such a way that the resulting number is greater than 5 but smaller than 9.

Can you find the missing number in the third row?
35 20 14
27 12 18
5 2 ?

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

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?

Find the mistake in the below maths equations

A = 2
A(A-1) = 2(A-1)
A2-A = 2A-2
A2-2A = A-2
A(A-2) = A-2
A = 1

Can you think of any three-dimensional shape that comprises of exactly two surfaces?

The product of three consecutive numbers is 7980.
Then the sum of these consecutive numbers would be?

Find out the missing number in the picture attached:

Below, you will find the mathematical proof that 10 equals 9.99999?. But is that possible or there is something wrong about it? Can you find the error?

x = 9.999999...
10x = 99.999999...
10x - x = 90
9x = 90
x = 10