What is the fastest way to double your money?

Replace the question mark with the correct number in the below-given picture?

John and Jacob are twin brothers. One of them is a liar whereas the other one is a truth-teller.

I called their home number and one of them picked up.
I asked. 'Does John lie?' The person replied with a yes.

Whom did I talk with, John or Jacob?

Can you calculate the probability of getting a sum of six when a dice is thrown twice?

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?

Find the missing letter in the last circle logically in the given below picture.

12345 a famous South Indian actor
567 is a path in jumbled form
8 & 10 are same letters
9 is one among the first six alphabets.
WHO AM I?

Find the next number in the sequence

5 12 24 36 ?

I never stop running even when I standstill. If I am formed by joining two identical bodies together, can you guess who I am?

A girl has as many brothers as sisters, but each brother has only half as many brothers as sisters. How many brothers and sisters are there in the family?