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

Prove that twice of ten is the same as twice of eleven.

How many triangles are there on the puzzle below?

Two in a corner, one in a room, zero in a house, but one in a shelter. What am I?

Below the four parts have been reorganised. The four partitions are exactly the same in both arrangements. Why is there a hole?

If all Goats are Sheep and all Sheep are Deers, are all Deers Goats ?

We know that money can be names differently for the purpose it is used for. Some of the examples of money given at following places or for following activities:

In temple = Daan
In school = Fees
During marriage = Dowry
For divorce = Alimony
Paying government = Tax
In court = Fine
Employer to employee = Salary
To kidnappers = Ransom
For illegal reason = Bribe
To civil servant retirees = Pension

Do you know what do we call the money a husband gives to his wife?

I know a 5-digit number having a property that With a 1 after it, it is three times as large as it would be with a one before it.

Guess the number?

A mile-long train is moving at sixty miles an hour when it reaches a mile-long tunnel. How long does it take the entire train to pass through the tunnel?

I am an odd number. Take away a letter and I become even. What number am I?