Exchanging from 1
When a calculation involves exchanging from a 1, there may be a misconception that you can’t exchange that 1 as it would then leave zero. Pupils who lack confidence when calculating with zero may be particularly prone to making this mistake.
In example 1, the pupil realised that exchanging from the 1 would result in them having to work out 0 – 6 next and as that can’t be done, they bypassed the 1 and exchanged from the hundreds instead. They need to understand that you must always exchange from the next digit unless it is a zero.
In example 2, the pupil correctly exchanged the 1 ten, but failed to write a zero in the tens column as a placeholder. This resulted in the hundred which they next exchanged, becoming 1 ten instead of 10 tens, which meant having to exchange a further hundred to make 11 tens. They need to realise the importance of using a placeholder to maintain place value.
Base 10 equipment can be used to reinforce the importance of place value and how to maintain it through correct working.
See our How To video for an example of this.