Model and apply the associative property of addition to aid mental computation, eg 2 + 3 + 8 = 2 + 8 + 3 = 10 + 3 = 13

1. Back to School: 5c + 15c + 7 c
2. Add these 3 numbers: 8 + 3 + 2
3. Add these 3 numbers: 9 + 1 + 6
4. Add three numbers: 10 + 12 + 8
5. Add three numbers: 13 + 9 + 7