Month: July 2012

Mental addition and subtraction for year 4

Here is a real mixture of addition and subtraction questions which can all be answered mentally without resorting to written methods. The questions include adding 2-digit multiples of 10 to 3-digit numbers and subtracting 2-digit multiples of 10 from 3-digit numbers.

Interestingly, some of the addition statements can be answered by subtraction and some of the subtraction statements can be completed by addition. For example: 35 + ?? = 75 can be done by subtracting 35 from 75. An equally good method would be to add on in tens from 35 to 75.

In the same way 36 – ?? = 20 can be completed by adding on from 20 up to 36, or simply by subtracting 20 from 36. This all helps with understanding the relationship between addition and subtraction.

This set of worksheets, which because it involves both addition and subtraction is slightly harder than just dealing with one, can be found in the Year 4 addition category.

More addition and subtraction practice

 

Year 3 Mental Arithmetic: sets 69 and 70

A final look at addition and subtraction with these two sets of ten mental arithmetic questions for year 3. By the end of the year children should really be developing their mental arithmetic strategies, which are almost like ‘tricks of the trade’. Let’s take a look at a few of them which crop up in these questions.

1. 34 add 35 can be done in several ways such as adding the tens then adding the units and adding the two totals. Another way is to double one of the numbers and adjust by one e.g. double 34 is 68; add one to make 69.

2.  603 – 590. My favourite way to do this is adding on: add 10 to make 600 and then add 3 more to make 603. Answer is 13. This is much easier than trying to subtract 590 from 603.

3. subtract 9 from 265. This is one they should be very familiar with; take ten and add one. Of course some children will count down 9 using their fingers, but this will be much slower.

Year 3 mental arithmetic: sets 69 and 70

Subtracting using the standard method

Children need plenty of practice at using the standard written method of subtraction if the are going to become competent with it and calculate without making errors. This is a nice little page as it concentrates on subtracting 2-digit numbers from 3-digit numbers.

More than this the questions are graded in difficulty, according to the rows, so it also makes for an excellent assessment sheet to see just how well they are doing.

The first row is very straightforward, with no adjustments necessary.

The second row questions all require adjustment from tens to units and the third row requires adjustment from the hundreds to the tens.

The last row is the real tester as it needs adjustment from hundreds to tens to units. Watch out for the common erro, such as saying that 0 – 6 is 6.

This page is part of the collection of subtraction worksheets found in the Four Rules category.

Standard subtraction of 2-digits from 3-digits