To think that this sum is super simple

[PeerieBreeks]

and can't understand how so many people on Facebook have it so completely wrong (and can justify it to themselves).

Without adding your reasoning, tell me what you think the answer is.

So
-60
+70
-80
+90

equals 20

By jove I think I've got it!

YABU This is not simple. My 15 yr old thinks $10 ?

When my 7 yo has a word problem maths question, I always get him to pick out the number sentence first. So
-60 + 70 - 80 + 90 =

Assume balance is $0
buys horse first time ... bank balance is minus $60
sells horse first time ... bank balance is plus $10
buys horse second time ... bank balance is minus $70
sells horse second time ... bank balance is plus $20.
So he made $20.
Simples.

And it would have been a nice surprise for me, because I originally thought I had broken even.

Not that I would have passed the test.

I think it's reasonable to suppose that we are only required to calculated the EBITDA for this problem. So, sure Revenue can take their cut later.

Are you suggesting that if he did it all using cash, he wouldn't declare his earnings to HMRC. Is he some kind of cowboy?

Sagethyme

The problem with this question is you have to assume the man has a minimum of $70 to start with

Why?
You could say he starts at 0
0-60- -60
-60+70= +10
10-80= -70
-70+90 =+20
Difference between 0 and +20 is 20

Or you could say he starts with 44
44-60=-16
-16+70=54
54-80=-26
-26+90= 64
Difference is still +20 (64-44=20)

You could assume the man has any amount to start with and you should always get the same answer.

running thanks.

That was in response to sagethyme. Gosh, this thread moves fast!

I spent the last years of my teaching life trying to get disinterested, belligerent, frankly terrified by maths 16 - 19 year old to see that Marcine

It really is worth parents getting to understand the types of questions in maths these days. This and the BIDMAS types seem to cause all sorts of issues, and they really don't have to.

It isn't the teachers fault, apparently they have to teach specific 'procedures'. So I used to get kids who knew 4 different ways of working out long division. My favourite was a grid with each box / in half. All students could put the right numbers round the outside, but none could complete the sum. Many could partially do 2 or 3 different methods!

No wonder they hated maths and often had to fight back tears when forced to attend my classes.

Can you guess why I 'retired'?

@runningoutofjuice, those blocks remind me of the cuisenaire rods that we had at school when I was a child

Totally off topic, but Curious, your name has bought back memories. Family holiday when I was a child in Norfolk, seeing these signs saying "S A M P H I R E" - maybe a samp was some kind of flat-bottomed boat (cf punt) and you could hire it to explore the local marshes etc? The truth was much better, and I enjoyed tucking in to some freshly cooked samphire once we realised!

@purplerobe it's still not a loss in the middle. If he started with 60, then when he pays 80 he clearly owes 10 to someone, but then he ends up with 90, less the 60 he started with is 30, less the 10 he owes is 20.

£20

-60
+70
80
+90
= 20

He is down £60 on the purchase = -60
He then sells for £70 so = + 70 which = +10
He buys again for £80 so = -£70
Sells again for £90 so = +£20

@alpineibex I love that you are now explaining it absolutely correctly to someone else :)

*-80

dadx3

upside because presumably if you start with nothing you have to borrow? I should add I am no mathematician but surely logic dictates if you start with zero where do you get $60 from? You have to borrow it.
I completely get the answer by the way, but I can also see why others are getting a differen result. In fact taking it at face value it would make much more sense to have just the numbers without the language. The language is the issue because the assumption is the man starts with $60, he therefore needs to borrow $10, he'd then need to give the $10 back, therefore his profit is $10, unless of course he does as dadx3 suggests and has no fines/ interest to pay in which case profit is $20....
And this is why I hate doing my tax returns!

So - 6 +7 - 8 + 9 = 2

Feeling like a genius for once!

so
-6 + 7 = 1
-8 + 9 = 1

add the two together and you get

2

PeerieBreeks

Thank you. Numbers definitely take a while to 'click' in my head.

It’s the fact that it’s the same animal involved in each purchase and sale that is confusing people, I think. If I said that a farmer went to market and bought a pig for $60 and a goat for $80 and sold a sheep for $70 and a donkey for $90, and asked how much more money the farmer had in his wallet at the end of the day people wouldn’t be as bamboozled – but the calculation required would be identical.

He buys a horse for $60. 0-60 =-60
He sells the horse for $70 -60+70=10
He buys the horse back for $80 10-80 =-70
He then sells the horse for $90 -70+90=20

He's gained $20