- #1

m0bius

- 15

- 0

So this isn't a homework problem I suppose, but this seems to be the best place to post. I've been going through the online math subject GRE, trying to first identify what field of math I will need to solve the problem, then figuring out how to solve them. However, the test covers a wide range of fields. About 50% of the test is Calculus and Differential Equations, 25% is Linear Algebra and Abstract Algebra, and the rest could be from any other subject including Analysis (real and complex), Topology, Probability, Combinatorics, etc...

So, there have been a few problems where I cannot even identify which math to use.

For how many positive integers k does the ordinary decimal representation of the integer k! end in exactly 99 zeros?

There are 5 answers to choose from : 0, 1, 4, 5, 24.

There have been some types of problems I've never seen before, but have been able to figure out using various fields of math. I have never seen a problem like this before and I don't have a clue of what math to use. My guess is that it has to do with Real Analysis, but it also sounds like a Number Theory problem.

If somebody could at least point me to a field of math to use that would be great. I never took a course in Topology, Combinatorics, or Probabilty. I'm about to start learning the basics of those, but if the problem requires any of them it would be great if you could point me towards a theorem or something. Thanks!

So, there have been a few problems where I cannot even identify which math to use.

## Homework Statement

For how many positive integers k does the ordinary decimal representation of the integer k! end in exactly 99 zeros?

## Homework Equations

There are 5 answers to choose from : 0, 1, 4, 5, 24.

## The Attempt at a Solution

There have been some types of problems I've never seen before, but have been able to figure out using various fields of math. I have never seen a problem like this before and I don't have a clue of what math to use. My guess is that it has to do with Real Analysis, but it also sounds like a Number Theory problem.

If somebody could at least point me to a field of math to use that would be great. I never took a course in Topology, Combinatorics, or Probabilty. I'm about to start learning the basics of those, but if the problem requires any of them it would be great if you could point me towards a theorem or something. Thanks!

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