Wanna know a trick for this? If you're not familiar with what I call the

**"log trick of 3's"** then read this first:

http://forums.studentdoctor.net/showpost.php?p=6412828&postcount=3
So knowing that -log(3 x 10^-q) = ~ (q-1).5 such that -log(3 x 10^-5) = ~4.5

I messed around in Wolfram|Alpha one day and realized this trick works another way:

If you have an expression where 10^-q, then the trick of 3's holds, just in reverse.

10^-5 = 1 x 10^-5

10^-5.5 = ~3 x 10^-6

10^-6 = 1 x 10^-6

10^-6.5 = ~3 x 10^-7

and so on. So for a value like 10^-3.7, I would note that the decimal 7 is greater than 5, meaning the value of the mantissa is below 3, and the exponent is 10^-4. Conclusion is that 10^-3.7 = <3 x 10^-4

This should be accurate enough to identify the answer needed, if this is a terminal step in solving a problem.