I have already told to some guy here. The real numbers are divided to several groups. The division that is of interest to us is the division between the rational and irrational numbers.
Rational numbars are numbers that can be writen as the division between two whole numbers. For example, 2 is Rational number as it can be writen as 10/5 or 12/6 or -4/-2. The same goes to the number -1.5 which can be written as -3/2.
Irrational numbers are numbers that can't be written as the division of two whole numbers. This is the case with the square root of 322. The point is that the only acurate way to write an irrational number is keep it as it is (322^0.5 is our case).
One thing of interest is that you rational numbers that are fraction can be either writen either with finite number of digits or with repitation of a string of digits (1/3 = 0.3333333... and 1/6 = 0.166666....). Irrational numbers on the other hand can't be writen in the same way, if you try and calculate the 322^0.5 you won't get a repitation of a digit.
If you made some calculation and have reached that result, leave it as it is because you this is the most accurate and elegant way to show this number. If you need to perform some calculation with it leave it as it is. If, you are at school and you have to show some results the way brosen has writen is answer should be sufficient but bear in mind what I have just wrote.