My friend Charles works in a post office and he sells stamps. One day a man walked in and slamming seventy five rupees on the counter requested,
"Please give me some 2 rupees stamps, six times as many one rupee stamps, and for the rest of the amount make up some 5 rupee
stamps."
Charles thought for a few moments and finally she handed over the exact fulfilment of the order to the man.
How did he do it and how many stamps of each type did he give to the man ?
Let x be the number of 2Rupee stamps. Let y be the number of 5Rupee stamps.
Our equation is
2x + 1*(6x) + 5y = 75
So, 8x + 5y = 75
Since the 5y part of the equation will yield only numbers ending in 5 or 0, then so must the 8x part of the equation. Check for values of x where 8x is divisible by five.
when x=5, 8x=40
when x=10, 8x=80; already the total cost for the stamps has been exceeded, thus x must be five.
By substitution we find that 5 2Rupee stamps, 30 1Rupee stamps, and 7 5Rupee stamps where purchased with no change left over.
postage
