Whats amused you (in the news) today ?

where are you getting 9/2 ?

It wasn't a million miles out, just slipped a decimal place...

£1.80 winnings off a £4 stake is equivalent to £18 off £40, or £9 off £20.  So the odds would be 9/20 in this example (rather than 9/2). 
Interpretation: "You stake £20 and, if you win, I will give you £9 back, plus your original £20.  If you lose, I keep your £20".  

Traditional bookmakers rarely offer 9/20 odds, though, to the best of my recollection.  They would likely offer one of the more customary prices 4/9 or 40/85, which lie either side but are close enough to 9/20 to make no practical difference. 

The newer exchanges deal in tighter margins, so offer decimal odds which are easier IMHO to deal with.  

The progression of odds, 4/9, 9/20, 40/85 would be presented as 1.44, 1.45 and 1.47.  Much easier to see what's going on.  [You add 1 to the fraction shown, so 4/9 = 0.44 in decimal terms, becomes 1.44.  9/20 = 0.45 becomes 1.45 and 40/85 = 0.47 becomes 1.47.  It's now clearer that the three very different looking odds are all pretty close in fact]. 

With the newer bookies like Betfair Exchange, which I use for my tiny wagers for fun (sports, politics, but no interest in horses), it's very common to see the odds 1.44 or 1.45 or 1.47 being offered, and the odds drifting freely between the three as money gets wagered in real time, for or against the event concerned. 

Taking the middle figure of 1.45, the interpretation is now: "You stake £20 and, if you win, I'll give you back £20 x 1.45.... = £29.  If you lose, I keep your £20".  Identical to the traditional 9/20 odds outcome, possibly easier to understand and certainly easier (to me anyway!) to calculate more complex multiple bet payouts, such as Yankees, Trixies, Accumulators, etc.  

Going back to the original post, winning £580k off a £400k bet, that would have required odds 580/400 = 29/20 - not 9/20 note, but 29/20 - which is 1.45... or in decimal odds on the Exchange, 2.45.  The starting price when the flag dropped for this horse, the favourite, was evidently 6/5 (= Exchange odds 2.2), so it's most likely the gambler took an earlier price of 2.45, which later shortened to 2.2 as the race approached.  This will often happen when a horse is paraded just prior to the race and looks really "up for it".   

Subsequent to benaj 's original post, there's a suggestion here that the story was wrongly reported all along and the stake was actually £600k rather than £400k.  I haven't the heart to recalculate... life's too short... so I leave that as homework for you dear reader  .
community.betfair.com/horse_racing/go/thread/view/94102/31795879/400k-on-energumene--tony#flvWelcomeHeader#flvWelcomeHeader

Well, I have never place a ££££££ single bet in real life.

Assuming not all bookies will take that amount at EP, early prices, he will have to visit bookies everywhere and get his best prices for his large stake.

He could also been staking his bet over a long period with different amount different odds. 2/1 , 15/8, 7/4, 13/8, 6/4 ….

and possibly laid his bet in running. It doesn’t cost him much to lay 1.01

So the SNP has a choice of a man who does not know there is a war in Europe. A woman who is a member of the wee-frees (bonkers religious group) and a woman no one has heard of.

Meanwhile the Kremlin funded Salmond lead party must be preparing a coup

Bit late to be telling us that now.

I thought I'd done well with a decent 12/1 but I only had £5 EW