Easy peasey, my math teacher stated when you multiply two odd numbers, you get an odd number.
Surprised someone managed to find that first one to work!
3*4 = 3√16 = 16/3 = 5.3333333
3*8 = 3√64 = 64/3 = 21.33333
3*6 = 3√36 = 36/3 = 12
4*10 = 4√100 = 100/4 = 25
2*4 = 2√16 = 16/2 = 8 Got it!
This trick only works if the first number is the square root of the second:
3*9 = 3*(3*3) = 3* (3*3)*(3*3) => (3*3)*(3*3)/3 = (3*3)*3 = 9*3