The number is 42.
Let xy be the number. x is the tens digit, y is the units digit. The ratio of the units digit to the tens digit, y/x, is 1/2. This gives us the proportion
y/x = 1/2
The tens digit is 2 more than the units digit; x = y+2; substituting in our proportion we have
y/(y+2) = 1/2
Cross multiply:
y*2 = (y+2)*1
2y = y+2
Subtract y from each side:
2y - y = y+2-y
y = 2
x = y+2
x = 2+2
x =4
xy = 42
