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.

He started off with 60

I'm afraid that is your mistake, nowhere is that stated, it's an assumption.

bruffin - but he lost $10 in the middle buying it back, so net result $20.

I've got maths A-level and I think there's an argument for saying that he made either 10 or 20.

Sorry, blackberry, to do this, but I've got two Maths A-levels, a first class Maths degree, qualified as an actuary and work full-time in Finance. The argument for $10 doesn't stack up.

My pictorial illustration upthread encapsulates what many have said. If you physically follow it through with dollars in the pocket, you end up $20 better off than you started. No clever accounting arguments required.

Its 30
He started off with 60 and ended up with 90

Nope. In that case he wouldn't have been able to afford the horse when it sold for 80.

He made the profit when the horse increased in value from 60 to 70.
So he made 10.

Someone else made the profit when the horse increased in value from 70 to 80.

He made the profit when the horse increased in value from 80 to 90. Another 10.

Ergo, he made 20 profit.

I agree with all the others who say it's a logic, interpretation problem rather than a maths problem

Yes i realised that a minute after i posted

Dad, those diagrams make it look so complicated! To make it simple, say he starts the day with $70. He spends 60 so still has 10. He then sells for 70, so now has 80. He spends the entire 80, so now has nothing! He sells for 90 which means he is $20 better off than when he started.

He makes a $10 profit on each sale right. So $20

BitOutOfPractice true, and as we don't know the time periods between transactions, we could add in all sorts of other issues, is he borrowing to fund this, what about any earnings he makes from horse ownership, does he invest the initial $10 profit etc?

However, we can only deal with the facts presented, this is primarily a logic and reasoning issue, the mathematics are a side-show.

I love reading the explanations for the answers, it’s fascinating to see how other people’s minds work.

But, in all honesty, this is quite worrying. Those of you getting it wrong, don’t you get yourself in a lot of trouble in the real world?

I get that not everyone is good at everything, there’s plenty I’m properly crap at or have no interest in, but this isn’t high level maths. It’s very basic. Do you not constantly end up in financial trouble?

20 ? But I want to say 10 emotionally / instinctually for some weird reason.

Dad, those diagrams make it look so complicated!

They're not complicated but they do make it look long-winded.

Unfortunately, many have given the kind of succinct and perfectly correct explanation that you have given, but others still are saying $10 or $30. I was trying to show it step by step for those people, but I don't expect anyone will bother.

I love this thread (partly because I got $20, which made me feel smug, which is - after all - the point).

I agree that the sum is simple, but the wording clouds this.

It helps that I've been going through worded maths problems with DS this week, who spends most of his time shouting things like "but WHY would anyone drive from Cornwall to Scotland to deliver two curries? WHY??????"

20 up

People saying £10 are , I think, taking off £10 to buy the horse a second time, when they don't need to

But 8 agree we dont know whete he got the extra £10 as it may have been a result of investing the original £60 when he sold the horse the first time.

Surely the spiritual anguish of this series of transactions costs him at least a tenner. So net profit would feel more like $10.

My instant response was $20 profit. He spent $140; he gained $160.

Then I over complicated it, and reasoned. -
1st transaction $10 profit;
2nd transaction $10 loss
3rd transaction $10 profit

Overall profit $10

It's that second transaction which is tripping me up. I think I am assuming he has borrowed $10 and therefore has to repay it to someone else - is that the trap I'm falling in to?

if your maths fails you, use teaspoons or 10p pieces (each worth 10 dollars) and “sell” something to your dc with the spoons - see how many more spoons you have at the end than the 7 you needed to buy the original ‘ほrせ

IShould Yes, I know that but my friend here with me, who put forward that scenario, wasn't convinced, which was what I found interesting and is why we are still discussing our relative confidence in maths!

Wow I dont know how my horse did that

Surely we need to know how much he started with to know what he made?

There is still the problem of the $10 loss. He'd have to somehow negate the loss against the profit to have a truer sense of profit in real terms not as a hypothetical maths problem. Losses do have to be put in context of profit

20

baking That has really rattled my brain... I can't make any sense of it at all

@Ifailed of course you know I was joking don't you?

The profit figure also depends on whether he's reporting to the bank manager to get a loan, or the tax man