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

Count the number of triangles in the picture below:

I have cities, but no houses. I have mountains, but no trees. I have water, but no fish. What am I?

Can you find the next number in the below sequence
3 , 7 , 10 , 11 , 12 , 17 ?

Be active and find the killer in the picture Riddle below.

Two boys wish to cross a river. The only way to get to the other side is by boat, but that boat can only take one boy at a time. The boat cannot return on its own, there are no ropes or similar tricks, yet both boys manage to cross using the boat.

How?

A bank customer had $100 in his account. He then made 6 withdrawals. He kept a record of these withdrawals, and the balance remaining in the account, as follows:

Withdrawals Balance left
$50 $50
$25 $25
$10 $15
$8 $7
$5 $2
$2 $0
----- -----
$100 $99

Why are the Totals not tallying?

If we tell you that there is a relation between the numbers and letters in the given figure, can you analyze it and find the missing letter in the last box?

They came out at night, without being called.
They lost at day, without being stolen.
Who are they?

I speak without a mouth, and hear without ears. I have no-body, but I come alive with the wind. What am I?