Mentally adding and subtracting multiples of 1000, 100, 10 or 1 to a 4-digit number. Comparing different ways of representing 4-digit numbers. Unconditional probability.

Slide 1 of 4, Kelly writing on a chalk board 'step 1'. She is stood next to a subtraction sum under TH, H, T and O columns. 4328 − 1436. All the numbers are faded apart from the 8 and 6 in the O ...