### Brain Teasers

# 1000 Prime Numbers

Determine the ones place value of the product of the first 1000 prime numbers. (What number would be in the ones position if you multiplied all of the first 1000 prime numbers together?)

### Hint

All you need to know the first three prime numbers.### Answer

ZERO. Any numbers multiplied by 2 and 5 (which are prime) result in a zero in the ones place.Hide Hint Show Hint Hide Answer Show Answer

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### Solve a Puzzle

## Comments

Good one! Had me really puzzled until I tried the first couple of products. Sneaky!

If I would have tryed to solve it yesterday, it would be much harder. Yesterday I knowticed that for avery n>5, n! will have '0' in ones position. I thought about that. 2*5=10 and any number multiplyed by 10 will have '0' in the end. And here is practicly the same case.

How could somebody who notices something like that not notice how they are spelling words?

Sorry I have no Math sense!

I am math stupid, so I didn't get it

eeeeeeeeeeeeeeeeezzzzzzzzzzzzzzzzzzzz

I did not get that!

that was ok

What???

i ain't good at math ..............................plus i thought it was boring

ps cat y don't u do that ur self ..........

ps cat y don't u do that ur self ..........

wont a 5 be in the one's place if you multiply 5 by an odd number?

That is only right if you have to multiply them all in order. Which is pretty much implied, but still.

This was like doing my taxes. I did not even feel like trying to solve this...it is more like a chore than a puzzle.

All that for nothing...literaly... zero?

But i'm sure the math buffs liked it.

All that for nothing...literaly... zero?

But i'm sure the math buffs liked it.

Bookmidget, the result is the same regardless if the order the numbers are multiplied.

Good teaser. For a couple seconds it seemed hard, but by the third second I had the answer.

Good teaser. For a couple seconds it seemed hard, but by the third second I had the answer.

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