Which sequence correctly describes DEA number validation?

• A. Multiply all digits by 2 and sum.
• B. Add digits 1, 3, and 5; add digits 2, 4, and 6 then multiply by 2; add these two numbers; last digit should match the DEA number's last digit.
• C. Sum all digits and take the modulo 9.
• D. Check that the first digit equals the last digit of the DEA number.

Answer: (B)

DEA number validation uses a check-digit method to catch common input mistakes. You look at the numeric part after the two letters (the seven digits). Add the digits in the odd positions of the first six digits (positions 1, 3, and 5). Then take the digits in the even positions (2, 4, 6), sum them, and multiply that sum by 2. Add these two results together. The last digit of that total should equal the check digit, which is the final numeric digit of the DEA number (the 7th digit of the numeric portion, i.e., the overall last digit). This is exactly what the described approach does: it sums digits 1, 3, and 5; sums digits 2, 4, and 6 and doubles that sum; adds the two results; and checks that the last digit matches the DEA number’s last digit. The other options don’t follow this check-digit procedure (they use inappropriate operations or wrong digits).