Today we're carrying on our mental strategies; ways to make sums easier in your head. This one is called the 'bump' strategy, and once you've understood it, can make sums a lot quicker.
Here's an addition, 18+31. You could do this in your head with the split strategy from yesterday - there's nothing wrong with doing that. But you could do it like this, and find it easier.
So, because 31 is very close to 30, let's bump it down to 30. So now we've taken1 from the sum.
That 1 from the 31 we've stolen, we'll give it back - but to the other number. So we'll give it to the 18, make it 19.
Now we've 19 + 30, all you do is add 3 to to the tens of 19, 49, job done! It sounds like 'swapping' the one around would give you the wrong answer, but as long as you give that one back after you've pinched it from the other number the answer will be the same.
Neat little trick isn't it? See if you can use it to solve your Mathletics today - Bump Add and Subtract.
Why not let me know which you prefer, the split or the bump?
If it's a subtraction, you've got to adjust the first number by the same amount, like this: