105
One.
5 and 7 are prime numbers. and 3 goes into 9, so the only number that goes into 5, 7, and 9 is 1. They are what we call "relatively prime", even though 9 is not prime, because they have no common factors other than 1.
As 3 and 5 are Prime numbers, no other number will go evenly into them. (presuming that "evenly" means a multiple of two). If you are looking for a common factor of 3, 4, and 5, then the answer is 1.
The only number that goes into both 3 and 4 is 1.
5 3/5
105
1, 3 and 5
3/5
1, 3, 5, 15.
One.
15/5=3 100/5=20
1, 3, 5, 15.
1, 3, 5 and 15
1, 3, 5, 15.
1, 3, 5 and 15.