The commutative property is true.
Also, odd times even is even; odd times odd is odd; even times even is even.
All multiples of 9 have digits which sum to 9 or a multiple of 9.
All multiples of 5 end in zero or 5. (Even multiples of 5 end in zero, and odd multiples of 5 end in 5.)
All multiples of 10 end in zero.
All multiples of 3 have digits which sum to 3 or a multiple of 3. All multiples of 6 are even and have digits which sum to 3 or a multiple of 3.