I was spending the morning helping Ernie dig up the potato patch when he got an emergency phone call from the Society for Absent-Minded Mathematics Professors – it appeared that they had “A bit of a problem”. So we both headed over to see how we could help. When we arrived, the club’s officers were all gathered in the main office looking flustered. The secretary told us that “There was some good news, and some bad news”, and when Ernie asked for more explanation, we heard the following story.
“We have been a little short of funds to pay the rent on the club-rooms, so we decided to have a fund-raising open-day”, said the secretary. “Unfortunately, I forgot to post out the invitations, so only four guests came to the event”. And he pointed to four business cards resting on the table. “But fortunately, they each donated a very generous sum of money – more than enough to pay next year’s lease!”.
“They each wanted an invoice for their donation (they have to file tax returns by 5:00 pm this evening at the latest)”, continued the treasurer. “Unfortunately I couldn’t find the receipt book, so I promised them that we would write down their names and how much they donated, find the receipt book, and get their receipts to them before the tax office closed. But fortunately, we have now found the receipt book.” And he waved a scruffy pink pad in the air.
“For safekeeping, I locked the record of their donations in the strong-box, along with the money”, continued the Vice-President. “Unfortunately, in trying to open it again, I set off the time lock – so we won’t be able to access the record of who paid what for the next 24 hours. But at least the money is safe”.
“And after I called you, and we were awaiting your arrival”, said the president, “each of our patrons phoned to let me know that he or she had absent-mindedly left an item behind, that it had great sentimental value, and could I please drop it off with the promised receipt (and each reminded me that it was vital that their receipt arrived before 4:00 pm). Unfortunately, I had been so flustered by the previous events that I didn’t make a note of who had left what. But fortunately” she said, gesturing at a small pile of belongings, “at least we have found all four articles”.
“Well the last thing you would want to do is to disappoint your generous patrons by messing up their tax returns. But I’m sorry”, said Ernie after examining the safe. “Short of a large stack of dynamite, we won’t be opening that in a hurry. But maybe between the four of you, you can recollect enough for us to work out who paid what – and to whom each item belongs. Tell me exactly what you remember”. And the club officers made the following four statements:
President: “The lowest two donations made up more than one third of the total amount donated. The Count made his donation immediately before the Solicitor made his. I can’t remember how much each person donated, but I am positive that one donation was at least two-thousand dollars more than one of the other donations, and that no single individual donated more than ten-thousand dollars. Curiously, each made their donation in used one dollar bills – when I checked the total amount after all four had donated, the total sum was exactly divisible by 1000.”
Treasurer: “I kept a running sum of the amount donated. I can’t remember the numbers any more, but immediately after the Doctor made their donation, the total at that point was an odd number. One of the donors kept sipping from a small hip flask and another kept fiddling with a cheap plastic key-chain – I can’t remember which was which, but one of those two was the Barrister, and the other one donated an amount with an odd digital sum. The donations, in the order they were made, formed an arithmetic progression. I can’t remember much else, except that when I calculated the digital sum of each of the four donations, those numbers were not all prime numbers”
Secretary: “I was using my new calligraphy pen for the first time today. I thought it was curious that when I wrote the donors names down I had to write every letter of the alphabet from a to z at least once. Come to think of it, when I wrote down the individual amounts they had donated I also had to write every digit from 0 to 9 at least once too. The donor with the fancy gold pocket-watch made their donation some time after the donor with the mirror-lens sunglasses.”
Vice President: “Each of the donations was a prime number of dollars. In fact, now I recollect thinking, that had the entire total been converted into one thousand dollar notes, there would be a prime number of bank-notes. I think the musician wore the sunglasses – or maybe they were the one with the brandy flask – actually can’t remember which was the case, but I’m certain it was one of the two.
Ernie thought for a while, then quickly scribbled out four receipts, placed a business card and an item from the pile of lost-property with each one, glanced at his watch and informed the club officers that they would need to hurry if they were going to get the items to the correct recipients before the 4:00 pm deadline. I can only guess that Ernie must have super-powers, because without seeing the record of donations or hearing the President's phone calls, surely there is no way he could have worked out who donated what, and who owned each item. I am right aren’t I?