Maths question

Carl_Scope

If you were asked to do the sum 17 + 18, how do you get to your answer? What's the process in your mind?

Do you add the tens first? The digits?

I know maths isn't everyone's cup of tea, but even if we all get the same correct answer, the way we get there seems to vary a lot and I find that really interesting.

So how do you work it out?

OverlyAnxious

I'd start with the largest number, then add the tens, then the digits.

18+10=28

28+7=35

But, there's another method I'd use if they were larger numbers. Particularly with tens adding up to more than 100 and digits adding up to more than 10.

I can see it's just +3 and +2 to make 20 in each case (=+5). 20+20=40. 40-5=35.

Looks complicated but I find it's more reliable when going over 100 in my head.

Rosie_Scope

I would look around the room for someone else and hope they worked it out before I have to 😅

But really, I would add 7 & 8 together (usually with my fingers 🤓) then add the 10+10

Bluebell21

I would add 18 +18 = 36 - 1= 35

Kimi87

7+8 =15

10+10= 20

15+20=35

StarryEyed

Add the 10s, so 10 + 10 = 20

Add 7 + 8 = 15, and add that in two steps:

Add the 10 of the 15 = 30

Add the 5 of the 15 = 35

WhatThe

Right to left

Dynamisante

17

+
18

=
(7+8 =15 add the 5 carry over the 1

1 add 1 add the 1 carried over = 3, so you have 35,

I was taught math at grammar school a long time ago, I positively know how things have changed as helped my 4 children with their math along the way 😂

StarryEyed

Four children???? 🫪🫪🫪🫪

damine222

I do 17 + 3 = 20 first, then add the remaining 15. Rounding to a ten makes the rest easy.

Carl_Scope

I've genuinely found it so interesting the different ways we all do it.

https://forum.scope.org.uk/discussion/comment/1150609#Comment_1150609

I do it the same as you @Bluebell21.

I asked a family member though and they said the same as @Kimi87's, 7+8 then 10+10.

I'm curious if it's to do with when or the way we're taught in school or if it's regional or something else more individual.

OverlyAnxious

I wouldn't be able to add two 18's in my head any more quickly than 17 & 18.

Did you learn the 18 times table?

Carl_Scope

https://forum.scope.org.uk/discussion/comment/1150740#Comment_1150740

I think if I broke it down, what's actually happening is I see '18' and jump to the 9 times table.

So I'm reading 18 as 2 9's, so 18x2 is 9x4 which I know without calculating

OverlyAnxious

https://forum.scope.org.uk/discussion/comment/1150745#Comment_1150745

Ah, that's interesting.

Sad to say I wouldn't know 4 x 9 off the top of my head either, so would still have to do some calculation for that. (Or use the finger method…but that only works for 9's!)

Thinking about it, I'm not sure I'd immediately know that 18 = 2 x 9 in a quick mental maths situation either. 😐️

I've always been alright at maths, but struggled to do it mentally without writing anything down. I think different brains just process information differently. I could probably work out more complex calculations than the average person. But they'd most likely be quicker than me at adding up the bill for a meal!

WhatThe

By right to left I meant @Kimi87's method..

https://forum.scope.org.uk/discussion/comment/1150752#Comment_1150752

The beauty of the 9 times table is that the answer always adds up to 9!

3x9=27 7x9=63 9x9=81

Carl_Scope

https://forum.scope.org.uk/discussion/comment/1150752#Comment_1150752

Yeah, I wasn't a big fan of maths at school but I had my times tables drilled into me very early on so that's the only thing I remember now!

Mary_Scope

I couldn't do this in my mind, I'd need to get a pen and paper and do long maths!

I'd add the 7 and 8 first, get 15, carry the 1 over and then add 1+1+1 to get 3 which would make it 35 overall😄