Sometimes it is much easier to carry out a calculation mentally (in your head) than to use the standard written method. This page of questions illustrates this perfectly. It looks at taking a one-digit number away from a multiple of a thousand.
if this was written down on paper it would involve considerable amounts of crossing out and ‘borrowing’ from thousands to hundreds and then from hundreds to tens; a potential minefield for children. However, if they just count back from the whole thousands, even using fingers to check that they have counted back the correct number, hey presto, the answer is found in seconds.
Similarly, with a question such as 4 000 – ??? = 3993 adding on can be employed: start with 3993 and counting on until 4 000 is reached. Simple.
This page can be found in our Year 4 Calculating category.
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