We have a great many reasoning maths worksheets in Year 4 and have just published a further set on rounding. Rather than just asking for a particular number to round, the questions give rise to several possible answers. For example:
I have two different numbers.
They both round to 30 when rounded to the nearest 10.
The sum of the two numbers is 59.
Find all the possible combinations of two numbers that I could have.
To fully answer this question children must show a good understanding or rounding to the nearest whole 10 and be able to work in a systematic way.