What does this mathematical rebus means ?

Here is a mathematical expression that also secretly tells a movie name. What movie is that?

Cristina was born in 1888. She just had her 30th birthday today how did that happen?

When is the top of a mountain similar to a savings account?

John was running from 40 thieves. John has got 3 gold boxes which weigh as 4kg, 2kg, and 1kg respectively. A witty man asked John to stay with him for seven days in exchange for 1kg gold per day. John needs to stay there for seven days and also do not want to give the witty man any advance. How can John pay for his seven days stay?

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?

Spelt forwards I’m what you do every day, spelled backwards I’m something you hate. What am I?

What's a single-digit number with no value?

What always comes into a house through the keyhole?

Solve this tricky question. You are trapped in a forest. With you, you have a gun preloaded with two bullets in it. In front of you, there is a tiger, a leopard and a jaguar.

How do you survive?