Otley All Saints CE Primary School Blog

Year 4 had fun showing off their ‘addition’ skills to Mrs Webster recently!  They could add up any odd number of consecutive (next-door-neighbour) numbers easily.

Here’s how they did it:

Find the middle number and multiply that number by the number of consecutive numbers in the list.  For example:

6+7+8+9+10 = 40

As there are 5 numbers in the list, we can times the middle number by 5 to get the same answer:

8 X 5 =40

Try it!

Remember it is easy to multiply a two-digit number by 9 or by 11.

To multiply a number by 9, first multiply it by 10 and then take away the number that you are multiplying. E.g. 23 X 9 = (23X10) – 23 = 230 – 23 = 207 – EASY!

To multiply a number by 11, first multiply it by 10 and then add the number that you are multiplying.  E.g. 23 X 11 = (23 X 11) + 23 = 230 + 11 = 253 – PEASY!

Now amaze your friends and family with your maths wizardry and let us know how you get on by ccommenting.

Mr Robertson

 This trick makes you look like your brain is a mega fast calculator!

Ask a friend to write down ANY three digit number such as 231 or 884. Ask them to multiply the number by

x 7 and then
x 11 and then
x 13

…but even if your friend has used a calculator, you will have written down the answer ages ago! It’s fiendish!
THE SECRET: all you do is write out the starting number twice! So 231 will become 231231 and 884 will become 884884. You don’t believe it? Try it right now then leave us a comment about how you got on! 

Ask a friend to think of a two digit number e.g. 391.

Now ask them to reverse this number e.g. 193.

Ask them to take the smallest number away from the largest number e.g. = 198.

Ask them to reverse this number e.g. 891.

Ask them to add the reversed number to the unreversed number e.g. 891 + 198 = 1089.

The answer will always (well nearly always!) work out to be 1089.  Amazing isn’t it?!  Leave a comment to let us know if you tried this trick and if it worked.

 Mr Robertson