I would appreciate help with a question form OCR book further pure 1
"An emerging currency has two kinds of bank note, one for 5 schenkels and one for 9 schenkels. Prove by induction that every account greater than 31 schenkels can be paid without change by using the 5 schenkel and 9 schenkel notes/"
My only ideas were to use the fact that it works for 32 up to 37 and say that every number greater that 31 is made up by one of those plus a multiple of five. But this is quite unmathematical.
Any ideas would be greatly appreciated!