What is binary-coded decimal and how is it used?

SOLVED: In this problem, you are to implement a BCD (binary coded decimal) to 7-segment gates. The inputs to this circuit are a 4-bit binary coded decimal BCD number: A, B, C, and D. The seven outputs each drive one segment of the LED display, as shown in the figure. The digits 0 through 9 are to be displayed according to the value of the BCD number input. Each of the seven gates should have as few inputs (fan-in) as possible.

Circuit Design of a 4-bit Binary Counter Using D Flip-flops - VLSIFacts