Using only 4$ and 7$ bills, you could pay any integer number of dollars, greater than 17.
Prove it.

Given two coprime numbers a and b, what is the minimal number M(a,b) such that any amount greater or equal to M(a,b) can be expressed as p*a+q*b (p & q non-negative integers)?

How much is M(37,38)?

(In reply to part 1 solution, plus examples of M(x,y) by Charlie)

silly me:

of course itc's a*b-a-b+1

Posted by Charlie on 2013-05-01 18:12:47