Iam a number between 30 and 50 . i am a multiple of 8. my greatest common factor with 25 is 5 what number am i ?

The number is both a multiple of 8 and is also divisible by 5. The easiest way to find a number which fulfills both of these requirements is to multiply 5 by 8.

5*8=40

40 also fulfills the required range between 30 and 50. 40 is the number you are looking for.