3 goes into 18 six times.
What you have there is 5/6 as 3 goes into 15 five times.
5/6=0.83333...
So what you could say is that 15 yards is roughly 83% of 18 yards.
Likewise you could just get your calculator out and figure out what 15/18 is as a decimal...
Turns out that it's 0.83333... as a decimal.
Once again, you've figured out that 15 yards is roughly 83% of 18 yards.
