# Homework Help: A kind of Fermi Questions

1. Dec 2, 2012

### Negi Magi

1. How many sands on the earth?

2. Hints: Using the Fermi estimation

3.

2. Dec 2, 2012

### Staff: Mentor

What did you do so far? Where did you run into problems?
What is "sands"? Do you mean grains of sand?

3. Dec 2, 2012

### Negi Magi

Yes, I mean the "grains of sand"

I do not really understand your first two questions.

4. Dec 2, 2012

### Staff: Mentor

From the board rules:
This is not a board where others do your homework. We can help you if you run into problems, but it is your homework.

5. Dec 2, 2012

### Negi Magi

Oh,yes. When I first saw this question, I have no idea about that. However, now I know that this question is a kind of Fermi questions, which need appropriate estimation.

But the problem is that I do not know how to start. There is another Fermi question, " How many Piano Tuners in New York? " , I can do that by using the estimation of the population of NY, the amount of pianos, the working time of Tuners, etc.

However, when I am asked for "How many grains of sand? ", I don't know what data should I use to estimate

6. Dec 2, 2012

### haruspex

One way to approach it is to think about what parameters, if changed, would radically change your answer. E.g. if all the sand grains were a million times smaller than they actually are, that would make a lot more of them. Would this alter any other information available to you? If not, having an estimate for average grain size will be essential.

7. Dec 2, 2012

### Dickfore

I found this short book on order of magnitude estimation rather helpful