What is the smallest two-digit positive integer such that the product of its two digits is one-half the integer?
ab =1/2[10a + b], solve for a, b
a = b/(2 (b - 5)), or:
b = (10 a)/(2 a - 1)
If you try the first few numbers, you will quickly see that:
a =3 and b = 6. So, the number is:
36. Because: 3 x 6 =18, which is 1/2 of 36.