Subtraction strategies to reduce maths difficulties

Posted on August 7, 2010 by admin

How to help your child understand subtraction

Children need to understand what’s happening to the numbers when they are subtracting. The easy, best practice strategies below are highly recommended. Introduce a new strategy with small numbers that can be easily visualised, particularly if a child has maths difficulties.

Algorithms are now seen as just one way to calculate…not the only way. This is because they do not help children understand anything about numbers. All they do is provide an abstract process. Many children have no idea when they’ve made a mistake because they can’t determine the ‘reasonableness’ of an answer. Try some of these alternatives and notice how your child’s understanding grows.

Subtraction can be thought of as addition

eg 21-18 = ?

If you think of this in terms of addition, then you would ask yourself what you’d have to add to 18 to get 21.  Much easier!

Add or subtract the same amount to each number to make the numbers easier to deal with

By rounding one of them to the nearest 10 or 100, the problem becomes easily manageable.

eg 19 – 4 = ?

Round 19 up to 20 to make it easier. Also add 1 to the number you are subtracting (4) to compensate. The problem becomes:

20 – 5 = ?

= 15

Another example of rounding:

22 – 15 = ?

Round the 22 down to 20. Also take 2 away from 15 to compensate.

20 – 13 = ?

= 7

With larger numbers:

238 – 123 = ?

Round 238 up to 240. Add 2 to 123  to compensate.

240 -125 = ?

= 115

Make small jumps using easy numbers along a number line

The number line can be real or imaginary. A real one is recommended for any child who is having a lot of difficulty with Maths.

It’s easy to draw one up on a piece of paper. Your child may be used to drawing them at school. If so, great. If he doesn’t know how, you can get him to help you to draw one. This will give him practice in numbering and labelling accurately. You can add to it as he starts working with higher numbers. Make sure the ‘easy numbers’ are highlighted, eg 0, 5 10 etc, and all the other numbers are also marked along it.

eg To solve the problem 27-19, you can start at 19 and make jumps to the easy numbers up to 27, or start at 27 and make jumps down to 19.

If you start at 27, the easiest jumps would be 27 t0 25 (=2), then 25 to 20 (=5), then 20 to 19 (=1)

Then add up the jumps: 2+5+1 = 8

If you start at 19, the easiest jumps would be 19 to 20 (=1), 20 to 25 (=5), 25 to 27 (=2)

Then add up the jumps: 1+5+2 = 8

Take away the hundreds, tens and ones in chunks

For children 10 years and older who are familiar with negative numbers on a number line.

eg:

408 – 351 = ?

Take away 300 from 400 (= 100)

Take away 50 (5 tens) from 0 (0 tens) (= -50)

Take away 1 from 8 (= 7)

= 100 – 50 + 7 = 57

eg 51-19 = ?

Take 10 (1 ten) from 50 (5 tens) (=40)

Take 9 from 1 = (-8)

40-8=32

eg 56-32 = ?

Take 30 (3 tens) from 50 (5 tens) (=20)

Take 2 from 6 (=4)

20 + 4 = 24

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How to help your child with Maths

Posted on December 13, 2009 by admin

Diagnosing problems with Maths

difficulty with maths

Let’s look at one of the three main areas to check in number, that is, how well your child understands number patterns. It’s essential to check at a fundamental level because Maths understanding builds on step by step. Often we don’t look back far enough and so a child still won’t ‘get’ it.

Check where he is with saying the numbers in order. You do this to find out if he understands the 0-9 pattern correctly. You can do this as a game. You take turns to say the numbers one at a time as high as he can go. If he can get past 109 to 110, that’s great because many children confuse the pattern there and say 109, 200. Keep going to find where it starts becoming difficult. Next check if he can read numbers correctly up to his point of difficulty, and then check he can write them correctly. For example, a typical error in writing numbers is 100, 1001, 1002 etc.

People often ask how far a child should be able to go at a certain age. Well, here’s a rough guide:

By 5 …forwards and backwards to 10, starting anywhere along the way

By 7…the same to 120

By 9…the same into the thousands

By 11…the same into the hundreds of thousands

Remember, of course, that you can’t expect a child to say larger numbers in order if he’s still struggling with smaller ones. Everyone has a different sticking point, and your goal is to keep helping your child move forward. So if it’s getting through the teens, help him practise by taking turns to say the numbers 13-19. And when he’s mastered this, set a goal to get from 19 to 29. Just practise a few numbers at a time. No need to keep starting from 1. If he’s sticking at 109, start from 105 and practise saying the numbers to 112.

Find out where he can say the numbers from in reverse order. You may be surprised to find your child finds this much harder. Take turns to go backwards by ones. I’m sure you’ll find that you’ll need a lower starting number than for counting forwards.

Next find out how well your child can count by 2s forwards and backwards. Most young children can get to 10 forwards, but backwards is a problem. Try starting at 1 and saying the odd numbers.

Check his counting by 5s, 10s, 3s etc next. Again he may be good at going forwards, starting from 0…but try starting from 1 or 2 and see what happens. Backwards too, of course.

This is one of the most important areas of Maths to work on if your child is not confident in Maths.

BTW I’ve worked with children on this  frequently and they love practising the numbers orally. They can see their own progress and they feel successful. That feeling makes them want to keep going!

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