Use all the odd numbers from 1 to 9.
Put one number in each box of the cross.
The numbers in each line of three must add up to the same total.
Find all the possible totals.
1 3 5 7 9
CUTTING THE WIRE
Jack needed some short lengths of wire for model-making. He bought three pieces, all the same length.
He cut one piece into 4cm lengths and had 1cm of wire left over.
He cut the second piece into 7cm lengths and had 1cm of wire left over.
He cut the third piece into 10cm lengths and had 1cm of wire left over.
What is the shortest possible length of each piece of wire that Jack bought?
SOLUTIONS Magic cross (age 5-7) The possible totals are 17 (with 9 in the middle), 15 (with 5 in the middle) and 13 (with 1 in the middle)
Cutting the wire (age 10-14) The shortest possible length is 141cm. The lowest common multiple of 4, 7 and 10 is 140. Since 1cm of wire was left over each time, each piece was 141cm.