Percent Change w/ Fractions

[griffin.811]

If I want to find the percent change between 2 ratios, say (9/108) and (3/20), can't I compute a common denominator (60), change the terms to reflect the common denominator, so (5/60) and (9/60), and then drop the denominator and compute the change as: (new-old)/old, or (5-9)/9? (assuming the 9/108 was the "new" ratio)

I saw a similar question, and the Manhattan explanation did the percent change, but computed the change with the full fractions so [(5/60)-(9/60)]/(9/60).

I guess it doesn't really take all that much time to do it either way, I just feel the simple way is less intimidating, and less prone to error.

Thanks

[RonPurewal]

They're the same, so do the one you like better.

To show that they're the same, just take the expression
(this/60 – that/60) / (that/60)
and multiply it by 60 on the top and bottom. The result will be the same as your preferred form.

More generally, all of the "over 60"s don't change the situation because we're concerned only with the magnitude of a change relative to the original value. So it's really just a matter of ratios.

[griffin.811]

Cool, thanks for the quick response!

[RonPurewal]

No problem.