Day 1 Teaching
Write 654 + 567. One child calculates answer using expanded addition, another using compact addition. Remind both children to leave a space before drawing the lines for the answer. When children have finished, compare their workings and answers. Write 478 + 245, and 837 + 367. Use your preferred strategy to calculate the two answers.
-- Add two 3-digit numbers, using expanded and compact addition methods.
-- Make two 3-digit numbers using dice. Then add the numbers using compact addition.
Day 2 Teaching
Write 426 + 217, 742 + 276 and 587 + 278. Children round each to nearest 100, then add to estimate the total. Repeat, this time children round each to nearest multiple of 10; then use addition of 2-digit numbers to estimate total. Give 1 addition to each third of the class to find an exact answer. Compare with estimates.
-- Think mathematically to use chosen digits to make two (or three) 3-digit numbers with a total as close as possible to 600 (or 1000). Use compact addition.
-- Estimate the total of two 3-digit numbers; find the exact total using compact addition.
Day 3 Teaching
Write 48 + 26 + 35. Agree we could do this by adding the larger two numbers (83) and then the smallest. BUT we can also use column addition. This is especially useful if we are adding four 2-digit numbers. Model both expanded and compact addition for 45 + 28 + 63 + 38. Here, we had an extra 20 to add to the 10s! Children have a go with 36 + 45 + 58 + 23.
-- Add three or four 2-digit numbers, using expanded and compact addition methods.
-- Estimate the total when adding three or four 2-digit numbers, then find the answer using compact addition.
Day 4 Teaching
Write 43, 86, 27, 36, 18, 54, 72 and 67. Look for 3 numbers that might have a total close to 100. They check using column addition. How did you choose your numbers? Rounding to the nearest 10 can help. Now choose 3 numbers with a total near 150. Check using column addition. Now choose 4 numbers with a total near 150.
-- Look for 3 or 4 numbers that children estimate will have a total near given multiples of 10.
-- Play ‘missing digits’. Children work out the missing 1s digit in addition calculations.
Day 5 Teaching
Add 3 numbers where the digits in each number are the same, e.g. 33 + 44 +55. Share answers; discuss observations. Ask them to choose other trios of similar numbers to check if this is always the case. Can we write a ‘rule’ to describe what happens with additions like these? If one doesn’t work, check! [If the answer is a 3-digit number, the middle digit is the sum of the two digits on either side - a function of this being one of a certain group of multiples of 11; If the answer is a 2-digit number, both digits are the same].
Use the in-depth, whole-class, problem-solving investigation– Investigating 11– as today’s group activity.
-- Investigate patterns when adding three or four 2-digit numbers that have a difference of 11, e.g. 89+ 78 + 67.