Can you think of a smallest +ve number such that if we shuffle the digits of the number, the new number becomes double the original number?

In a university, a professor gave a set of three problems to the three brilliant students of his class. See the image for the questions.

What jumps when it walks and sits when it stands?

What is the fewest number of coins that would be required in order to make sure each and every coin touches exactly three other coins?

If we add four times the age of John four years from now to five times his age five years from now we get ten times his current age.

How old will John be two years from now?

What's the best place to go shopping in the ocean?

In the following picture, E is going to slide the object down and as per the terrain and the physics, the round object is going to travel all the way till the end. Now, can you analyze who all people will die when it happens?

I have a head like a cat and feet like a cat, but I am not a cat. What am I?

Jenifer and Jesica are having a conversation.

Jenifer: I am definitely not over 30.
Jesica: I am 28 and you are surely 5 years older to me at least.
Jenifer: No, you are at least 29.

You are told that both of them are lying throughout in the conversation. Can you find their respective ages?

There is a number which when you multiply by 3 and subtract 2 from the result, then the resulting number is the reverse of the actual number.

What is the smallest number that stands true on the statement?