One of the most powerful tools children can have at their fingertips is the ability to double and halve numbers in their heads. These two maths worksheets look at doubling and halving 3-digit numbers.
A good approach to doubling a number such as 174 is:
1. double the hundred (200)
2. then double the 70 (140, making 340 in total)
3. then double the 4 (8, making 348 in total)
It seems that most people would tackle this by starting with the hundreds: the opposite of doing it on paper when you would start with the units.
A similar approach can be taken when halving 3-digit numbers such as 894.
1. halve the 800 (400)
2. halve the 90 (45, making 445 in total)
3. halve the 4 (2, making 447 in total).
There are, of course other, perfectly acceptable ways of doing these and it is always worth talking about different ways of reaching an answer. For example half of 894 could be done by halving 900 (450) then subtracting half of 6 (3) making 447.