105
One.
1
the number that goes into 5,7,8 is the number 6
They are all prime numbers, so the no whole number goes into 5, 3, and 7 evenly. However, if one assumes that "evenly" means a multiple of 2, and that we can use any number, not just whole numbers, then any fraction of the form 1/2N (where N is any whole number) will go "evenly" into 7, 5, and 3.
5 3/5
105
3/5
1, 3 and 5
1, 3, 5, 15.
One.
15/5=3 100/5=20
1
1, 3, 5, 15.
1, 3, 5 and 15
1, 3, 5, 15.