You can do this activity at home using card and paper or you can use the template attached to complete it within Seesaw. Cut out 15 cards and label them 1 to 15 Insert the cards into a triangle format, with 5 rows. The first row will have 1 card, The second row will have 2 cards, 3rd row will have 3, etc. Place the numbers 1 to 15 into a triangle so that each card is the difference between the two cards immediately below it, to left and right. The first three cards have been done for you. 5 is the difference between 9 and 4. (9 – 4 = 5) Discuss strategies. 15 must go in which row? Why? Simplify: Use less cards. Use six cards (1 to 6) and arrange them into three rows using the rules above.