Teaching and Group Activities for Understanding
Day 1 Teaching
Everest is the highest mountain in the world at 8848m above sea level. Display table of heights to descend from the summit to base camp (see resources). Use column subtraction to subtract 453m from 8848m to find the height of ‘The balcony’ (1 move). Stress aligning the digits to the right. Repeat for 8848 – 952 (two moves: 100s & 10s), then 8848 – 985 (two moves: 100s & 1s).
-- Use counting up (Frog) to find height differences between camps on Everest.
-- Use compact subtraction to calculate the heights of each camp on Everest; check each subtraction using addition.
Day 2 Teaching
Write 3000 – 2674 on the board. Model compact column subtraction to find the answer (make quite an ordeal of it!). What might be a more efficient way to do this subtraction? Draw out using Frog. Draft a line from 2674 to 3000 and use Frog to solve. MUCH quicker! Write 4002 – 3978. Discuss an appropriate strategy. Choose strategies for other subtractions, e.g. 5324 – 5297, 6542 – 4362, 9874 – 2344, 6000 – 5873, 4012 – 3679, 6124 – 5968.
Use the ‘Subtraction trios’ in-depth problem-solving investigation below as today’s group activity.
Or, use these activities:
-- Make and justify choice of Frog or column subtraction to find differences.
-- Make and justify choice of Frog, counting back or column subtraction to find differences.