Does anyone NOT know the 9 times table finger trick?

[DilemmaDelilah]

I was having lunch today with my DH and one of my grandchildren and we were idly trying to work out the weight of a McVities ginger cake. It doesn't have the weight on the packet, but it says that it has 9 portions each of 25.8g, so we were doing some mental arithmetic to work out the weight (for fun only... It wasn't performative grandparenting). Anyway - I was working it out the way that is easiest for me, which is to break the sum down into its component parts, i.e. 25x4, plus 25x4, plus 25, then 8 x 9 and add in the decimal point, then add them altogether which is, apparently, the autistic way (I am autistic) but seems ultra logical to me. This involved, obviously, working out 8x9. I did my usual finger trick to remember the answer and neither DH nor my grandson has ever heard of it!

It uses the fingers of both hands as a reminder. Bend down the first finger, that leaves 9 fingers, that means 1 x 9 is 9. Bend down the second finger, that leaves 1 finger and 8 fingers = 18, therefore 2 x 9 is 18. Bend down the third finger, that leaves 2 fingers and 7 fingers = 27, therefore 3 x 9 is 27 and so on....I thought this was something everyone knew, but apparently not! How about you lot? And does anyone else have any equally easy ways of remembering maths? My DH and grandson thought it was magic!

I'm amused about those implying it's a bit silly and people learnt by rote. I never learnt my times tables (too lazy probably) and actually I think because of it I have a better grip of number patterns as I use lots of tricks in my head to check numbers when multiplying.

Oh and I have a B in a level maths so clearly just above competent!

My kids taught me the finger trick and they use it all the time pretty quickly. No one would bat an eyelid in their age group (late teens) as everyone does it!

I do think we have to be aware that people might actually need this as some people do really struggle with maths and even learning by rote doesn't work. It's a bit mean spirited to pretend otherwise.

I’ve never seen the finger trick, but ^^this above is the way my primary school taught us to remember the 9 times table. Take the digit you’re multiplying by 9, subtract one, then add another digit that adds up to 9, eg:

6 x 9:
6-1=5 so 5 is the first digit of the solution
9-5=4 so 4 is the second digit of the solution
6 x 9 =54

8 x 9:
8-1=7
9-7=2
8 x 9 = 72

Yes I still do this!

I had heard of it.

I don't know my times tables. I just work them out in my head if I need to.

Yep, can't remember where or when I learnt it but I still find it useful.

I think you’ve highlighted the difference between visual and spatial learners and those that just memorise numbers. My DD is very dyslexic and very visual and any tricks that put numbers into physical space like the 9 x finger trick are essential! I still count on my fingers and visualise spatial counting tricks and did a physics MSc with loads of long maths equations. People just visualise the world differently and learn differently as a result. I would also do that sum exactly as you did but I’m not autistic.

Bend down the second finger, that leaves 1 finger and 8 fingers = 18

Granted it is late and my brain is not at its best, but I don't get this.

I have 10 fingers. If 2 are bent down how does that leave 1 finger and 8 fingers?
I get it leaves 8 (up), but where does the 'that leave 1 finger' come from?

Of all the times tables to need a trick, the 9s is not high on my list.
I pretty much know it in my head, but if I need to think, I know that the first number is one less than whatever I'm multiplying 9 by e.g. for 4 x 9 I know that the first digit is 3. Then I know both digits add up to 9 so the second one is 9-3=6. 4 x 9 = 36.

I'd love a trick for the 6s and 7s!

For OP's sum I would x 10 and then take away 25.8 (or more likely subtract 26 and add 0.2)

25.8 x 10 = 258
258 - 26 = 232
262 + 0.2 = 232.2

I have used this all my life!

I’ve never heard of the finger trick but I have heard of the up/down digit one a PP mentioned so you go 09/18/27 etc.

Although my favourite method of multiplying anything by 9 in my head is to multiply the number by 10 and take one lot of it away.

So 25.8 would be 10 x 25.8 is 258. Take away 25.8 which in my brain would be to take away the 25 from the 250 first as it’s rounder, so 225 and add the 8 back on so 233. Then take away the remaining 0.8 so 232.2

Yes I know this trick. My mum taught me so I never learnt the 9x timetable. It’s a great trick.

Never heard of it

but I love it

I just tried it out

Yes this, I’ve never heard of it but the references to extra fingers have confused me. I also don’t need it having been a chant and learn 80s kid.

Yes, I thought everyone had memorised their timetables to 12

@Phase2 and @rosemarble you ONLY bend down the second (or third or fourth etc. ) finger, not the first and second fingers. Try it. Put both your hands out on a table (or whatever) in front of you. Look at your left hand. If you are timesing 9 x 2, bend down the finger second from the left (your ring finger). That will leave your little finger (1) then a gap where your second finger is bent down, and your remaining fingers will add up to 8. Thus, 1 and 8 = 18 (not literally of course - I am well aware that 1+8=9).

I am extremely glad that I'm not the only person who would have worked out the sum in that way! To me it's very logical. Most people will know that 4 x 25 = 100. So 9 x 25.8 is 2 lots of 4 x 25 - easy peasy 200, plus another 25, easy peasy 225, then the slightly more tricky bit of working out 9 x 0.8 - which is 9x8, or 8 x 9 using the finger method, = 72 and then putting the decimal point back in, 7.2 and adding it on. 225 + 7.2 = 232.2. To me that is much easier than 10 x 25.8 = 258 which is, admittedly, easy, then taking off 25.8 which is much more tricky to my mind. However that is just how my mind works.... You do it whichever way suits you.

Yep have used it since learning it at primary.

I went to primary school in the 70s so learned to throw paint creatively rather than rote learning of times tables.

Nope never taught it in school. Born in the 70s
we memorised our times tables

I’d never heard of this. But it’s 6am (where I am) and I’ve just explained it to dh 😂

For your original calculation, I would have done 9 x 25 plus 9 x 0.8. I find it fascinating how all our brains work differently.

Edit: But I may well have unconsciously split it into two lots of 4 x 25 plus 25. Interesting 🤔

I was taught this in primary (35 years ago) & have used it since. It’s actually pretty helpful when you need it

dont know it
i would calculate 25 times 9, by doing 25 times 10 and minus a 25
i like the fact that all the numbers divisible by 9, add to 9, ie five times 9, equals 45, and 4 plus 5 equals 9.

and the numbers go up and then down again, same numbers, different order
9
18
27
36
and later on 90
81
72
63

Never heard of the finger trick, went to primary school in the 70s, we had to learn out times tables up to 12 times table.
I haven’t got enough fingers for the trick anyway 🤣 (upper limb difference)

Times by ten is just adding a nought on the end, it’s almost instantaneous maths. I’m autistic, but find this way far more logical. Each to their own. If you learn up to 12 times tables by rote as a child it’s very useful.

Johnny Ball used to drain the life out of me as a kid.

Never heard of it, I had to memorise tables as a young one. But it sounds interesting!

Same. It was like more school, after school.