just curious to know if its ok to write powers of a number as decimals or if they have to be fractions in order to be marked as correct in an exam.

e.g. a^1/2 * a^2

is it correct to write the answer as a^2.5 or does it have to be a^5/2 in an exam.

(the answer in the back of the book was a^5/2 but id like to know if it would still be marked correct in an exam if you wrote it as a^2.5)