The ones in the subtracted number should be greater than or equal to the ones in the second to avoid a renaming problem. For example 56 - 34 is fine but 57 - 29 is not. Problems like these are delayed until the students have part-whole thinking.

Using Materials

Examples. Word stories and recording for: 45 – 21, 52 – 23, 42 - 32 35 – 14, 63 –
61, 38 - 28....
 

Using Imaging

Shielding and Imaging Only examples. Instant recall of single digit subtraction facts is needed here. Word stories and recording for: 46 – 24, 55 – 25, 43 – 12, 37 – 21, 34 – 13, 46 - 41....

Using Number Properties

Examples. 97 – 10, 78 – 30, 20 + 62, 46 + 50, 80 + 17....
Challenging examples. The students will need to understand the meaning of three
digit numbers to do these. 240 – 20, 340 – 40, 443 – 20, 570 - 20....