Surely you jest...
A base 10 measurement system is rife with fractional results.Since 10 has only three factors, 1, 5, and 2, there's few calculations in that space that won't result in fractional results. Really clumsy fractional results since 10 can only be subdivided easily into 10ths, 5ths and halves.
The reason, or at least one of them, that there's twelve inches in a foot is that 12 has factors, 1, 2, 3, and 4. It can be simply subdivided in to 12ths, 6ths, 4ths, 3rds, and halves. The probability of any calculation yielding an integer result is far more likely than with a base 10 system.
The original question, how is 4/15 of 100 calculated has two primary approaches.
One is to treat is as a ratio as was done in post #3. That would be 4 is to 15 as X is to 100, or restating it as 4/15=x/100. The solve for X. X=4*100/15 or 26.666...
The other is to simply understand the notation. 4/15 means 4 divided by 15. Then the problem is stated 4/15 * 100/1=X. Which actually is a step in solving for X in the ratio statement but doing it this way doesn't require any pesky algebra. Albeit the trivial amount needed to solve the ratio.
Actually the ratio approach is far handier. What if you had an image with an aspect ratio of, say, 23 high by 35 wide and you wanted to reduce the height to 14. What would the new width be? Just state it as a ratio...
35/23=X/14 or 14*35/23
It works the same if you want to make the width, say, 43. What would the new height be?
23/35=X/43 or 43*23/35
Thus endeth the lesson.
