Two friends, Joe and Smoe, were born in May, one in 1932, the other a year later. Each had an antique grandfather clock of which he was extremely proud. Both of the clocks worked fairly well considering their age, but one clock gained ten seconds per hour while the other one lost ten seconds per hour. On a day in January, the two friends set both clocks correctly at 12:00 noon. "Do you realize," asked Joe, "that the next time both of our clocks will show exactly the same time will be on your 47th birthday?" Smoe agreed. Who is older, Joe or Smoe?
To find the answer, we have to find how long it will be before the clocks show the same time again. This is when the slow clock loses six hours, and the fast one gains six hours. This will take 90 days. In 90 days they will come together at 6:00. On a calendar, there are 90 days between noon January 31, and noon May 1 in years with no leap year. If Smoe had been born in 1933, his 47th birthday would have been in 1980, a leap year. This means that Smoe must be older, born in 1932, and the time of this problem is 1979.
Today's brain teaser courtesy of Braingle.com.