The average cost of 3 greeting cards is $4. The total cost of 2 of the cards is $6.80. What is the cost of the third?
3 x $4 =$12 Total cost od the 3 cards
$12 - $6.80=$5.20 The cost of the 3rd card. So that:
$6.80 + $5.20 =$12 /3 =$4 The average of the 3 cards.
