The Sunday Telegraph - Sunday - - Front Page -

A SE­RIES OF MATHS-BASED PUZ­ZLES BY DAVID WELLS For My Next Tick… I have no watch but I have an ex­cel­lent clock, which I some­times for­get to wind. Once when it had stopped for some time, I restarted the clock and then went to the house of a friend for the evening. I was quite jeal­ous hear­ing the chimes of the ever-ac­cu­rate grand­fa­ther clock in his hall­way. As soon as I got home I set my clock to the right time. How could I do this with­out know­ing the length of my trip? An­swer at the end of Puz­zles. THAT’S CU­RI­OUS… Buy­ing from your favourite store, you are of­fered a dis­count of 5 per cent for pay­ment in cash, 10 per cent as a reg­u­lar cus­tomer, and 20 per cent be­cause it is sale time.You can take the dis­counts in any or­der, with the se­cond dis­count be­ing cal­cu­lated af­ter the re­duc­tion for the first dis­count, and so on. In what or­der should you take the dis­counts in or­der to pay as lit­tle as pos­si­ble for your pur­chase? An­swer at foot of col­umn. David Wells’s lat­est book is Games and Math­e­mat­ics: Sub­tle Con­nec­tions (Cam­bridge UP £15.99)

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