Books of prime entry — practice question

After a trade discount of $20\%$ and a cash discount of $2\frac{1}{2}\%$ had been deducted, a customer paid $\$15\,600$ to a supplier. What was the invoice amount entered in the purchases journal?

• A$\$12\,480$
• B$\$15\,600$
• C$\$16\,000$
• D$\$20\,000$