Anyone listening to the Today programme on Radio Four might have spotted the Isle of Man theme to their ’Puzzle for Today’.

Set by the School of Mathematics at the University of Manchester, the tricky challenge goes as follows:

’You have two pound coins from the Isle of Man.

’You place both coins on a flat table and in contact with each other.

’If you roll one coin completely around the outside of the other, maintaining contact between the coins, but not allowing any slippage, how many steps will the Triskelion on the moving coin have taken?’

Stumped? Yes, we were too. Especially when we checked our pockets and purses and nobody could find a Manx £1 coin with a Triskellion on it.

We asked Colin Campbell, investment and banking manager at the Treasury, to clear up this extra puzzle for us and he was happy to oblige, explaining that this £1 coin had been issued to coincide with the millennium.

He told us: ’It was issued in 2000 and was actually called the Millennium Bells coin. There are bells between each of the three legs.

’Before that you have to go back to 1978 for a coin issued with the triskellion on it.

’That was called the Percy and was a thinner coin: those are very rare now.’

He added that you would expect a coin to be in circulation for around 30 to40 years after its issue so there are still plenty of Millennium Bells around.

But there are 10 other designs currently in circulation too, which clearly cuts down your chances of getting one in your change.

We also spoke to Professor Andrew North from the School of Mathematics at Manchester University who was responsible for setting the Puzzle for Today for Wednesday last week.

We asked how he came up with the idea for the puzzle and how he knew about the Triskellion.

He said: ’The puzzle is a minor variation on a relatively well-known problem, sometimes termed the coin rotation paradox.

’The basic idea of the puzzle, rotate one coin around another and see what happens, is relatively "classic" and isn’t mine. It was published in Scientific Amerian in the 1860s and later described by Martin Gardner, see https://en.wikipedia.org/wiki/Coin_rotation_paradox for an explanation.

’I decided to use Manx pound coins to make it a little bit different and slightly cleaner to state.

’The other reason for specifying a Manx coin is that I believe they will remain circular.’

He added: ’I have no particular Manx connections, but I have visited for holidays. I’m pretty sure that I learned about the Triskelion at School or from a book of Manx legends that I will have borrowed from the library as a child, but I can’t really remember.

’I met somebody with Manx connections at a party the other weekend which is what put me in mind of the coin when I was thinking up suitable puzzles for Today.’

Oh, and the answer to the puzzle? Here it is:

’The centre of the moving coin is a whole coin diameter away from the centre of the circular path, which means that the distance moved by the coin centre in a complete circuit of the fixed coin is twice the length of the coin’s circumference (2 Ï? d instead of 2 Ï? r).

’Hence, in order to move its centre the required distance the coin must rotate twice during its path and the Triskelion takes six steps.’

â?¢ The island’s Treasury is reminding residents that United Kingdom ’round pounds’ will remain legal tender in the Isle of Man after they are taken out of circulation in the UK next month.

In the UK the new 12-sided one pound is superseding the traditional round version, which is being demonetised from October 15.

This means it will no longer be accepted in UK shops but it can be returned to banks in exchange for the new coin.

The UK round one pound coins will, however, still be acceptable on the island alongside the Manx round pound and the new UK 12-sided pound coins.

Treasury member Bill Henderson MLC explained: ’In the Isle of Man we have not issued a 12-sided pound coin and we are closely monitoring the introduction of the new coin in the UK.

’The round UK pound coin will continue to be accepted in the island alongside the Manx round pound and the new UK 12-sided coin.

’As the UK round pounds are returned to the banks, however, they will be sorted and repatriated to the UK.

’Eventually the only pound coins left in circulation will be the Manx round and the UK 12-sided, making sorting much easier and ensuring greater visibility for the Manx coin, which will be around for several years to come.’