The BCD addition of 910 and 710 will give initial code groups of 1001 + 0111. Addition of these groups generates a carry to the next higher position. The correct solution to this problem would be to:

• ignore the lowest order code group because 0000 is a valid code group and prefix the carry with three zeros
• add 0110 to both code groups to validate the carry from the lowest order code group
• disregard the carry and add 0110 to the lowest order code group
• add 0110 to the lowest order code group because a carry was generated and then prefix the carry with three zeros