1. As shown in the figure on the right, there are four pairs ofnumbers that are opposite each other. The sum of each pairis 20. Since there are four pairs, the sum of the eight nenumbers is 20 X 4 = 80.2. Match the four pairs of numbers that are opposite each other. Make the twonumbers in each pair equal by subtracting a number from the greaternumber and adding it to the smaller number. Since all eight numbersbecome 10, their sum is 10x8 = 80.