In this picture shown, you will see these weird numbers that are dependent on IVs. Again, since you cannot see the number of a Pok?mon's IV, this will be hard. Usually, people use calculators like these:
MetalKid's Gaming resource, and
Serebii's. These two link will take you to a calculator that people use the moment they get the only perfect stat they need. For example, an Alakazam with 31/any even number/30/31/30/31. This means his best stats are HP, Special Attack, and Speed. This also mean he will be told by the guys who judges your Pok?mon's stat. Now he wants to make sure the others are even numbers since, again, he will not be able to see the exact IVs numbers. So the user has to train the Alakazam to at least level 50 exactly and not a level more or less in order to see his IVs spread on the calculator. Because the moment the Pok?mon reaches level 50, you must put on the calculator the current stats it has by then. Then the calculator analyzes and tells you the IVs spread. If it did come out with the correct spread, then he will get the Hidden Power type he wants. If you would like more proof on Hidden Power, you'll have to calculate with this method: Starting from 0, you will add number if the IVs is an odd number. If Sp. Defense IV is an odd number, add 32. If the Special Attack IV is odd, add 16. If the Speed IV is odd, add 8. If the Defense IV is odd, add 4. If the Attack IV is odd, add 2. And if the HP IV is odd, add 1. Now Alakazam's odd numbered IVs are Special Attack, HP, and speed. So we add 0+16=16+8=24+1=25. If you look at the picture from before, those from a range of 21 to 25 points ends up having Hidden Power Bug type.
Now in here, you will see a spread usually needed for ice and the most convenient spread most of the time.
Try calculating this on your own to see if you got the math part down.