PS i not sure if it belongs here but it didnt seem like it should go in the general fourm so i put it here

It's a pretty straightforward calculation. If you think of multiplying by hand, you'll end up adding stacks of ones. Each stack will have progressively more ones until the center, which has 9 (the number of ones in your two original numbers) and so you'll see that pattern.

Originally posted by UncleAdam nope, thats the way it came out on the calculator.

Then your calculator's defective. You need prime factors of 5 and 2 for a non-trivial number to end in 0, and 111,111,111 does not have either factor. The correct product is indeed 12345678987654321

Originally posted by TheMaster37 *cough* something ending in a 1 multiplied with something ending in a 1 ends in a 1. It's as simple as that 🙂

I agree with you, but apparently Bill Gates disagrees, as Excel does give the answer of: 12345678987654300. I was tuaght in school that any number ending 1 times any number ending in 1 gave a product ending in 1. But Bill Gates must be right - he couldn't possibly have gotten so stinking rich by being wrong... ..could he? 😉