Mathematics to the Rescue

 

It was my first day as a postdoc at MIT, and after landing at Logan Airport I took a taxi to a relative in Beverly, north of Boston, where I was going to stay for a few days while looking for a place to live for me and my family who were arriving a week later. The taxi driver had some difficulties locating the address and when we arrived the taximeter was on 34 dollars and fifty cents. “With the tip I will give you forty,” I told the driver and handed him a 100 dollar bill. “Sorry,” said the driver, “don’t you have smaller bills? I have only 40 dollars on me for change.” Hmm, I thought but could not find any small bills except for 10 notes of one dollar each. The problem seemed unsolvable. Can mathematics come to the rescue?

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Drachmas

“The fixed price to JFK is 28 dollars” said the taxi driver; “toll and tips not included, and I want the two dollars and seventy five cents for the toll upfront.” I reached to my wallet, dug eleven quarters and handed them to him. He carefully checked the quarters and said: “If you’re wondering why I want the toll money here, it is all because of the Drachmas.” “The Drachmas?” I asked. “Yes” said the driver. “They want to take me to trial for putting drachmas instead of quarters in the toll machine.” Apparently, using 100 Greek Drachma coins, which are almost of no value, instead of US quarters became quite a problem. “No matter how much I tell them that I put whatever the clients give me in the machine they still do not believe me, and want to bring me to trial. Therefore I now check the quarters the clients give me here in New York, in the light.” “I see” I said. I felt sorry for him. He was getting into serious trouble because of greedy, heartless passengers. 

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