Merchandise is ordered on November 10; the merchandise is shipped by the seller and the invoice is prepared, dated, and mailed by the seller on November 13; the merchandise is received by the buyer on November 18; the entry is made in the buyer's accounts on November 20. The credit period begins with what date

November 13

Step-by-step explanation:

Following dates are given

On November 10 = Merchandise ordered

Date of an invoice prepared, dated and mailed = November 13

Date when the merchandised received by the buyer = November 18

So, the credit period begins when the invoice is prepared, dated and the mailed by the seller to the buyer as it is the evidence of that the merchandise is ordered