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

Can you find the missing piece of the Porsche?

I am 5 letters long.
My first two tell you who I am
My first 3 could be a medicine
My last three reversed could be a young boy.
My 4th, 3rd and 2nd in that order could be a fruit drink.
If you have me you may hang me round your neck
WHAT AM I ?

Can you find the missing letter in the sequence?
S - T - I - L - ? - T - F - Y - C

Twice ten are six of us,

Six are but three of us,

Nine are but four of us;

What can we possibly be?

Would you know more of us?

Twelve are but six of us,

Five are but four, do you see?

What are we?

There is a box full of marbles,
all but two are blue,
all but two are green,
and all but two are red.

How many marbles are in the box?

There is a unique number which when multiplied by any number from 1 to 6, we will get the new number that contains the same digits only.

Can you find that number?

Which English verb becomes past tense just by rearranging the letters?

In particular commonwealth games, a female participant won silver and gold medals for a single event.

How can this be possible?

John replied, when asked how old he was. In 2 years he will be twice as old as he was five years ago.' How old is he ?