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.

BUT if the man needed to spend his first $10 profit to afford the second purchase, surely that original profit is cancelled out and he’s left with an overall profit of $10

No.

Perhaps it would help you to think that the buyers, who paid the man 70 and 90, paid him in advance.

He was paid 70 to find a horse for someone. He spent 60 on the horse. So he made 10 profit.

Later another person paid him 90 to find them a horse. He went to the person to whom he sold the horse in the first place. He spent 80 on the horse. So he made another 10 profit.

$1 = 76p more or less at today's exchange rate, so he made £15.24 less any currency exchange fees; say he's paying £2 in fees that'll be £13.24.

He buys a horse for 60 so he is down to -60 dollars.

Then he sells the horse for 70 so he is up +10 dollars.

Then he buys the horse for 80 so that's down to -70 dollars.

Then he sells it for 90 so he's up 20 dollars.

$20 profit!

$20 profit...my maths is terrible but I’m totally confused how anyone gets anything else...

Thank you Beehived - perfect explanation.
Off to lie down now and give my brain a rest

You math is incomplete because you forgot he lost $10 in the 2nd purchase.

Here’s the breakdown by transaction:
1st transaction he bought horse = $-60 loss.
2nd transaction sold $-60 horse for $70 = $10 gain.
3rd transaction had $70, bought horse back for $-80 = $-10 loss (bc he had to add an additional 10 to his 70 to meet 80).
4th transaction had $-80 horse but sold for $90 = $10 gain.

in the end, he gain $10.

@Mjenlew you bumped a five year old thread?

And bumped it with the wrong answer as well.

-60
+70
-80
+90

He made 20.

My above math is correct.
But so is this:
$60 loan to get horse, sell horse for $70, pay off $60 loan, have $10 profit.
Now have $10, need $70 loan to buy $80 horse. Then decide to sell horse for $90 and pay off $70 loan which leaves me with $20.

I think this guy needs to make up his mind about whether he wants the horse or not…

Where the money comes from to fund the purchase of the horse is irrelevant.

You just add up the credit and debits and the answer is always $20, because maths.