Does this always work? - Why? 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 .. 1 + 3 + 15 + 17 = 36 4 x 9 = 36

Aim Investigate Observe Prove

Spot The Difference 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 .. 15 16 17 18 25 26 27 28 35 36 37 38 45 46 47 48 15 16 17 18 25 26 27 28 35 36 37 38 45 46 47 48

15 x 48 = 720 18 x 45 = 810 810 – 720 = 90 Spot The Difference 15 16 17 18 25 26 27 28 35 36 37 38 45 46 47 48 15 16 17 18 25 26 27 28 35 36 37 38 45 46 47 48 15 16 17 18 25 26 27 28 35 36 37 38 45 46 47 48 Starting Point 10 Columns 4 by 4 square Answer = 90 18 x 45 = 810 Next Steps Investigate Observe Prove 810 – 720 = 90