0

The sum of face values of two coins is twice the difference of the two. Find them.

My math professor gave us a brain teaser, but I am extremely confused on how to solve it. I am aware that it might be a April Fool's joke, but he still wants a solution.. I know that one coin must be three times the other.

Caleb Stanford
  • 45,895
user137980
  • 33
  • If they were banknotes, see http://en.wikipedia.org/wiki/Three_Dollar_Bill – egreg Mar 25 '14 at 22:10
  • There must be several (circulating and historical) world currencies which have one denomination of coin which is three times the other: the Bahamas, for one. This really is off-topic for math, it takes nothing more than Wikipedia footwork. – Erick Wong Aug 19 '15 at 07:44

1 Answers1

6

A ratio of three is a rarity in coinage systems. They tend to use $1,2,5$ and things like that. I thought to check the old British coinage, because I knew it had funny values. Sure enough

In the years just prior to decimalisation, the circulating British coins were the half crown (2/6), two shillings or florin (2/-), shilling (1/-), sixpence (6d), threepence (3d), penny (1d) and halfpenny (½d).

So my answer would be a threepence and a penny.

Ross Millikan
  • 374,822
  • That makes sense! thank you so much. It kinda also explains the pirate theme. – user137980 Mar 25 '14 at 21:48
  • 1
    There may be other systems that have a ratio of three as well. I didn't try to find them. With the pirate theme, you might also think of six and two out of pieces of eight which in childhood I was told could be broken into eight pieces. But it seems not to be so. – Ross Millikan Mar 25 '14 at 21:54