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

A 52% bias toss for head using the 51% tail bias coin was done to obtain a fair result.

Can you find how bias is the floor in this case?

The person who makes it has no need for it. He who purchases it does not use it. The person who does use it does not know they are. What is it?

Why is the Hole below a Lock?

A brand new Mobile Phone was on sale at 20% as a promotional offer. By what per cent must the Mobile price be increased to sell it at the original price again?

What has one eye, but can’t see?

On my way to St. Ives I saw a man with 7 wives. Each wife had 7 sacks. Each sack had 7 cats. Each cat had 7 kittens. Kittens, cats, sacks, wives. How many were going to St. Ives?

He runs but never walks. Murmurs, but never talks. Has a bed, but never sleeps. And has a mouth, but never eats?

Solve the following series:
AZ, GT, MN, __, YB

When you say goodbye, I am what you need to tie.
I come as a couple and go wherever you run.
Who am I?