1) January 4, 2016, receipt of an invoice for a purchase of $1,000.00 plus $50.00 of GST (Goods and Services Tax)

To calculate the total amount of an invoice that includes the purchase price and GST (Goods and Services Tax), you would follow these steps:

1. Determine the purchase price: In this case, the purchase price is $1,000.00.
2. Determine the GST amount: The GST is $50.00.
3. Add the purchase price and the GST: $1,000.00 + $50.00 = $1,050.00.

So, the total amount of the invoice, including the purchase price and GST, is $1,050.00.