Math CentralQuandaries & Queries


Question from Kenneth:
To change a number to a percent, move the decimal two places to the right and add a percent sign. For example, 0.35875 = 35.875%.
If the number has a dollar sign or some other kind of unit,
for example, pounds, feet, etc. how is the number converted to a percentage.
For example, change $0.35875 and 0.75 lbs. to a percentage.
How is this done. I have never seen $35.875% or 75 lbs.% before.

Wonderful! You shouldn't. Percentages are for "dimensionless" numbers, numbers that have no units attached.

What you can do is convert a ratio of dimensioned numbers that have the same unit (or type of unit); the units cancel when you take the ratio.

So for instance $0.14 is 2% of $7 [14c/700c = .02 = 2%], 3 cm is 30% of a decimeter, and if your time to run a kilometer reduces from 4 minutes to 3 minutes 36 seconds [240 seconds to 216 seconds] it has improved by 10%.

Good Hunting!

You could also say that $0.35875 is 35.875% of a dollar or that 0.75 lbs is 75% of a pound.


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