addition | Maths Blog

Resource of the Week: Add 9 mentally

Being successful with mental arithmetic is all about having a ‘feel for numbers’ and being able to manipulate them to suit the way you like to calculate. Knowing a few basic ‘tricks’ helps enormously with this and gives children confidence.

Adding 9 might sound a little dull, but knowing that you can do it in your head by adding ten and subtracting one can make all sorts of other mental additions easy, as we will see later adding 19, 29, 39 etc all follow the same path as do adding 18, 28, 38 etc; these tasks which at first glance might seem tricky end up being easy.

This is suited to year 2/3 children who are confident with adding single digits and can count up to 100.

Add 9 to 2-digit numbers

Resource of the Week: Addition of 4-digit numbers

This week’s resource looks at how to add larger numbers using written methods. Addition of two 4-digit numbers is usually done on paper, using the following standard method:

The method is to add the units first, put the units in the answer, and ‘carry’ the ten into the tens column. Then add the tens and continue in the same way into the hundreds and finally the thousands.

A clearer explanation is available on the first page of the worksheets, together with a page of questions, but briefly:

Looking at 5687 + 2546 the steps are:

Step 1: add the units

7 + 6 = 13

Put the 3 in the units below the question.
Then place the one ten below the answer in the tens column.

Step 2: add the tens
8 (tens) + 4 (tens) + 1 (ten) = 13 (tens)
Place the 3 (tens) in the tens column and the 1(hundred) in the hundreds column below the answer.

Step 3: add the hundreds
6 (hundreds) + 5 (hundreds) + 1 (hundred) = 12 (hundreds)
Place the 2 (hundreds) in the hundreds column and the 1(thousand) in the thousands column below the answer.

Note: there may not always be tens, hundreds or thousands to carry.

Step 4: add the thousands
5 (thousands) + 2 (thousands) + 1 (thousand) = 8 (thousands)
Place the 8 (thousands) in the thousands column.
Answer: 8233

Standard addition of 4-digits (pg 1)

Resource of the Week: Pairs that make 20

This week it is a page from our year 2 worksheets which looks at pairs of numbers which make 20. Before doing this children should be confident with, and know by heart, all pairs of numbers which make 10. Once they know these, pairs that make 20 becomes easy; just one of each pair is ten more e.g. 6 and 4: 16 and 4. Being able to work quickly with mental arithmetic is one of the keys to success in school as so much of the maths lesson today is carried out orally and children gain or lose confidence very quickly when answering in front of a whole class.

Know pairs that make 20 (pg 1)

Year 1 Maths: 3 in a row addition

urbrainy.com are coming up with some excellent resources for year 1, including this great little board game of strategy and knowledge of addition to play with your child. You will need 2 dice, 2 sets of 5 different coloured counters or cubes plus a calculator and the games sheet.

Decide who is to go first.Player one goes first and rolls the two dice. Add up the total and place a counter on a square showing that number. If the number has already been covered it becomes the next players go. Then player 2 has their turn. The winner is the first person to put three counters in a row, across, down or diagonally.

Dice: 3 in a row addition game

Maths worksheet: Add decimals mentally (2)

This is a follow up page to an earlier worksheet on adding decimals mentally. The approach is probably the same as adding 2-digit numbers, in that most people seem to do these ‘in their head’ by adding the units first and then adding on the decimals.

So, with 4.6 + 3.5 my thinking would probably go along the lines of:

‘4 + 3 is 7, making 7.6 plus point 5 which is 8.1’.

It is not the only approach, but is usually a very effective one.

Add two decimals mentally (2)

Year 2 maths worksheet: Addition investigation

Here we have a maths investigation on addition, suitable for year 2. There are four numbers shown. The task is to choose any three numbers and add them up. Each number can be used up to 3 times, but the total sum must not include more than 3 numbers. So the sum could be 2 + 2 + 2, or 2 + 4 + 4 etc.

How many different ways are there of doing this and how many different answers are there.

These mini investigations are all about logical thinking, trying things out, working in a systematic way, recording information and checking that results have not been duplicated. They should also be fun. Most young children will not work in a systematic way, will repeat results and miss results – that is to be expected. But, over time they should begin to develop these skills. This investigation is good at encouraging working in a methodical way, starting with the smallest numbers, or starting with the largest numbers.

Thanks to urbrainy.com for this contribution.

Addition: how many ways?

Maths Worksheet: Standard written method of addition with 2-digit numbers.

This is the second maths worksheet on addition using the standard method.

(It must be pointed out that usually 2-digit addition should be tackled ‘in your head’. The sum we are doing here can be done by adding 50 to 66, making 116 and then subtracting 2 making 114. However, to practise the written method it is often useful to keep to smaller numbers)

The method is to add the units first, put the units in the answer, and ‘carry’ the ten into the tens column. Finally add the tens and write in the total on the answer line.

Once the method has been clearly understood and a good knowledge to adding single digits has been achieved it should be possible to move onto harder 3-digit or 4-digit addition.

Standard written addition of 2-digit numbers

Year 2 Maths Worksheet: adding 3 small numbers (pg 2)

Year 2 Maths Worksheet: adding 3 small numbers

Here is a little twist on the usual adding three numbers type of worksheet. On this page the third number is missing but the answer is given. What makes this harder is that at least two mental calculations have to be made to reach a correct answer.

Probably the easiest way to do this is to add the first two numbers together and take that total away from the final answer.

Another way of doing this is to count back each of the two numbers in turn and a n umber line is provided for this method.

Adding 3 small numbers (pg 2)

Year 2 Maths Worksheet: know pairs that make 20

Here we have a straightforward maths worksheet on knowing pairs of numbers that add up to twenty. This is suitable for year 2 children or those who are already very confident with knowing pairs of numbers that make ten.

If these facts are not known there are several ways of working the answers out, including:

1. Counting on from the smaller number.

2. Counting on from the smaller number up to 10 and then adding another 10. (If smaller number is below 10.)

3. Counting back from 20, which is trickier.

A good follow up to this page is to ask how many different ways you can make 20 by adding just two numbers.

Know pairs that make 20 (pg 2)

Standard written addition with money 2

The second of our worksheets on using the standard written method to add money. Remember to keep the decimal points in a straight column when writing these out. it is also important to write down any zeros that occur in the answer – don’t just leave that column blank. Encourage neat setting out of these questions as it eliminates the possibility of adding the wrong numbers in a column.

I always encourage children to write a decimal point in the answer before they start the calculation as, if it is missed out, the answer will be incorrect however well it has been added up.

Standard money addition (p2)