Can you replace the question mark with the correct number?

A boy purchased a book from a bookkeeper and gave him $100.
The cost of the book is $50 but the bookkeeper has no change, so he gets the change from the next shop and returns the boy his $50.

After some time the next shopkeeper came with the $100 note and told the bookkeeper that the note was a fraud, so he took the money back.

How much loss did the bookkeeper face?

What does below science rebus mean?

Ag Ag Ag
Ag SPOON Ag
Ag Ag Ag

I am a word that begins with the letter “i.” If you add the letter “a” to me, I become a new word with a different meaning, but that sounds exactly the same. What word am I?

That attorney is my brother, testified the accountant.

But the attorney testified he didn't have a brother.

Who is lying?

Which alphabet letter is a question?

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

What can go up a chimney down, but can’t go down a chimney up?

No matter how little or how much you use me, you change me every month. What am I?

A man was telling some of his war stories to his grandchildren.
"When the World War I was on the verge of end, I was awarded for my bravery for I had saved a group of my men." He coughed and then added, "When we were fighting in northern France, an enemy soldier threw a grenade at us. Before it could explode, I picked it up and threw it away. For my act of bravery, right before the war ended, A General gave me a sword engraved with the words "Awarded for Display of Bravery and Heroism in World War 1"."

Hearing this, one of the grandson spoke up. "Grandpa, this is not a true story. It can"t be true!"

The truth is that it was not. How did the grand children know it?