How do you interpret the interquartile range? My data is: Q1: 8.5 Q2: 13 Q3: 17.5 IQR:9.  The math problem says to interpret the interquartile range.  I have no idea what this means or how to do it.  
 A: I tend to think of the IQR as the range of the boundaries of the "middle 50%" of your ordered observations, with 25% of your observations below, and 25% above.
Suppose you have a variable named $x$, and the observations of $x$ are: 
10, 12, 9, 9, 15, 5, 9, 11, 9, 17, 5, 7, 11, 16, 4, 18
These observations can be ordered from smallest to largest:
4,  5,  5,  7,  9,  9,  9,  9, 10, 11, 11, 12, 15, 16, 17, 18
Here are the "middle 50%" of the ordered observations (you can see that 1/4, or 25% of the observations are below this middle 50%—4, 5, 5, and 7, and another 25% are above: 15, 16, 17, 18):
4,  5,  5,  7,  9,  9,  9,  9, 10, 11, 11, 12, 15, 16, 17, 18
The easy thing about the middle %50 in the example above is that the number of observations is 16, and 16 is easily divided by 4. But we can still get the "middle 50%" by defining the 25% and 75% boundaries, which in this case are 8 (half way between 7 and 9) and 11.5 (halfway between 11 and 12), so the IQR in this example is 11.5 - 8 = 3.5.
A: Actual interpretation is difficult without some sense of what we're measuring (how does one interpret raw numbers, without even units, let alone what objects we're dealing with? In this case we don't even have the original values, just the quartiles, so there's almost nothing that can be said).
Some facts which you should already have: 
Interquartile range (IQR) is measured in the same units as the data
It is the range of the middle half of the data.
It tells you something about how spread out the data is (more spread data tends to have larger IQR), but it is insensitive to outliers (particularly compared to say the standard deviation).

So armed with that understanding, you're left to interpret the IQR of "9"-whatevers, and if all you've been given are the values of the median and upper and lower quartiles, there's only those numbers to compare it with.
You may be able to write a single sentence about it, but you probably couldn't get three sentences worth of interpretation.
