I have a five and a three-gallon jar. Assuming there is an infinite supply of water, how can I measure one-gallon water?

Replace the question mark with the number below given a simple math problem.

Why is a river so rich ?

John and his team plan to rob a safe. They got just one chance to break the code else the local police will be informed. Below are clues:
A) Exactly one number is perfectly placed: 9 8 1
B) Everything is incorrect: 9 2 4
C) Two numbers are part of the code of the safe but are wrongly placed: 0 9 3
D) One number is part of the code of the safe but is wrongly placed: 1 4 7
E) One number is part of the code of the safe but is wrongly placed: 7 8 3

I add 5 to 9 and get 2. The answer is correct, so what am I?

In an Art Gallary, When the clock hit 11 am, Artist hung the painting number 30. When it struck 4 pm, he hung painting number 240 and when it struck 7:30 pm, he hung painting number 315.

Can you determine, which painting number will he hang when the time is 9:20 pm?

You need to arrange three 7 and mathematical symbols to form number 1?

If in a code language, DISTANCE is written as IDTUBECN and DOCUMENT is written as ODDVNTNE, the how will THURSDAY be coded as in the same language?

It belongs to you, but other people use it more than you do. What is it?

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