Mental Arithmetic - A Natural Talent Or Can We All Learn To Be Good At It?

Mental Arithmetic - A Natural Talent or Can We All Learn To Be Good At It? Often my husband will say, "How did you get to that answer so quickly?" when adding lists of numbers. I reply "I don't know, I just do it in my head!" At school one strategy we are taught is to add numbers in columns going from right to left, starting with the place values of ones (or units), then the tens, then hundreds, and so on, having to carrying numbers over when the situation arises. E.g.

An easier and quicker strategy when it comes to mental maths, is to work left to right. We don't have to worry about carrying numbers over and can see the size of the number we'll end up with from the beginning, which is useful when working with money. Let us look at it written down:- Take two three digit numbers, 142 + 212. NB It's now thought that writing 142 + 212 in this way also helps with addition as it gives more meaning to the numbers. To do mental maths we work left to right, across each number place value (hundreds, tens and ones). Remember 142 in expanded notation is 100 + 40 + 2! And 212 is 200 + 10 + 2! Starting with the 1(100) in 142, add the 2(200) in 212 to get 300, add the 4(40) in 142 to get 340, add the 1(10) in 212 to get 350, add the 2 in 142 to get 352, and finally the 2 in 212 to give 354. So answer is 354.

It seems long winded written down this way so let's try another example, shortening the explanation to mirror what is going on in your head. Adding 189 + 261 would give 100, 300, 380, 440, 449, and 450. So 189 + 261 = 450. More useful in everyday life maths is used for adding up money, restaurant bills, shopping bills, entry tickets to the cinema, theme parks etc.

So let's add £2.62 + £6.34. Ignore the decimal point for now, and in the same way as above, 200, 800, 860, 890, 892, and 896. Now insert the decimal point two places to the left of the last digit, so between the 8 and 9 to give £8.96.

But usually shopping bills contain more than two items so how do you do mental maths with a longer list? Take £1.20 + £2.35 + £1.55 + £1.00. Still follow the left to right method, but also look for number bonds (two or three numbers when added together give 10, 1-9, 2-8, 3-7, 4-6, 5-5, 2-3-5 etc..) In our head we have 100, 300, 400, 500, 520 (pause and think 2 + 3 + 5 = 10) so we can go from 500 to 600 in one step, and lastly 610. Then insert the decimal point two places to the left of the last digit as before to give £6.10. How do we get good at this? We practise at every opportunity and Wow our friends! Happy Mental Maths everyone And Keep Counting!