Use systematic reasoning: set up the relationship between the digits, find the total, then divide.

The tenths and thousandths digits are equal. Call this value d.
The hundredths digit is 1 less than the thousandths digit: d - 1.
Sum of digits	=	d + (d - 1) + d = 20
Simplify	=	3d - 1 = 20, so 3d = 21
Each equal digit d	=	21 / 3 = 7
Hundredths digit	=	7 - 1 = 6
The number is less than 1, so the decimal is 0.767.