Monthly Brain Teaser and Januarys AnswerTuesday, February 7th, 2012
Last month you were left with this problem:
The managing director rang the payroll department and told the trainee who answered the phone that he needed by lunchtime without fail the average salary of the ten people who made up the management group. He rang off before she was able to tell him that the whole department was out on a training course, that she was the only one in the department that day, and that she did not have access to senior staff salaries. Nevertheless she knew that all the managers were at a meeting and at this moment should be on their coffee break. So she went to their meeting room and asked if they would please give her their individual salaries so that she could do the calculation. They made clear that in no way would they tell her, a young trainee, their salaries, and neither would they write them down anywhere in case the paperwork went astray and any of their colleagues discovered that one or two of them were paid much more than the rest. The trainee was, however, a resourceful young lady and, after a few moments thought, suggested to them a way by which she could get the information she needed without anyone having to write down his or her salary. The managers were perfectly happy with this and she got what she wanted before they resumed their meeting. What did she do?
The answer? She wrote a fictitious salary on a slip of paper, gave it to one of the managers and told him to add to it his own salary, then write the result on another slip of paper which he should give to another manager. That manager should add his salary to that figure and write the result on another slip of paper and pass that on. Each manager was asked to do the same. The last manager gave his calculation to the trainee who deducted her original fictitious salary, divided the result by the number of managers and – presto – she had the average salary of the management group, which she delivered to the managing director in good time. She should go far.
This month consider this:
A scientist is growing bacteria in a laboratory dish. Once a minute each bacterium divides into two. She places one bacterium in the dish at 9.30am. At 10.20am the dish is half full. At what time will it be full?
Answer next month.