### Teaching and Group Activities for Understanding

**Day 1 Teaching**

Use Spider on the 1-100 grid to demonstrate how we can add multiples of 10 to a 2-digit number, e.g. 46 + 30. Stress that Spider doesn’t have to count in 1s! Repeat, using Spider to subtract multiples of 10, e.g. 63 – 40.

**Group Activities**

-- Children play a game using Spider on the 1-100 grid to rehearse adding and subtracting multiples of 10.

**Day 2 Teaching**

Use a bead string to demonstrate how we can add multiples of 10 to a 2-digit number. Note that the 1s digit does not change. Repeat to show how we can subtract multiples of 10.

**Group Activities**Use the in-depth problem-solving investigation ‘The Number Square!’ from NRICH as today’s group activity. Or, use these activities:

-- Children use a 100-beaded line to add or subtract 20, 30, 40 or 50. They choose their own calculations to solve.

-- Some children investigate patterns when adding and subtracting given multiples of 10 to 2-digit numbers.