Expert: Richard J. Raridon - 7/27/2006

Question
Could you please define the term "to the correct number of significant figures"?

Please provide solutions to
(a / b)^ -2

E = K / 2mX
a. make X the subject

u = Mm /M+m
a. solve for M
Is there a rule for when the subject is the numerator and the denominator?

Answer
The number of significant figures indicates how accurately you know a value.  8 has one sig fig, 15 has two, 3.14 has three, 3.141 has four, etc.  When you combine numbers, the accuracy of the result can't be more accurate than the accuracy of the least known value.  For example, the equation for circumference of a circle is (pi)d, where d is the diameter.  If the diameter is 10 and you multiply it on your calculator by pi, you'll get 31.4159... but it's misleading to write all those numbers down.  Basically, your answer is 31.  
I don't know what you mean by solutions to (a/b)^-2.  That's equivalent to (b/a)^2 but that's about all you can do with it.  
X = K/(2mE)
For clarity, you need to write it u = Mm/(M+m)
you can rearrange that to get M = mu/(m-u)
There's no particular rule.