How do you write the mixed number 3 25 as in improper fraction?

3 25 does not mean a thing!!!!

If you mean 3 2/5 , then to convert to an Improper Fraction , we multiply the denominator to the coefficient and then add the numerator to the result.

Hence

5 x 3 = 15

15 + 2 = 17

Place the '17' over '5' , Hence 17/5 is the Improper Fraction.