1. The puzzle is to put the numbers from 1 to 7 into the boxes, so that the two straight lines of numbers add up to the same total. This total is known as the Magic sum. In this example, the Magic sum is 15 because 1 + 5 + 7 + 2 = 15 and 2 + 4 + 3 + 6 = 15

2. Complete the following puzzle using the numbers from 1 to 7. Remember that each straight line must have the same total. What is the magic sum this time?

3. Try to complete the puzzle so that the Magic sum is 17, still only using the numbers 1 to 7. Explain your thinking. Are any other Magic sums possible with the numbers 1 to 7? Explain how you can be sure.