1) Bob lives right next to a fire station and a hospital. He has gotten used to the sounds of ambulance and fire truck sirens at all hours. The two sirens are identical. One Saturday, when Bob was finishing his dinner, he heard what sounded like a truck go by, followed a few minutes later by the sound of a siren growing louder. Without looking out his window, Bob knew which type of vehicle had made the siren sound. What was it, and how did Bob know?
2) Rupert lives in a city dumpster tightly sandwiched between a fire station and a hospital. He always hears ambulance and fire truck sirens, and he knows they both sound the same. On February 29th of a leap year, Rupert was spelunking in the dark recesses of his home when he heard a siren. Immediately, before he could see what it was or tell which direction it was headed, he knew which type of vehicle had made the siren sound. What was it, and how did Rupert know?
Continue reading for the answers…
Don’t spoil the surprise without at least thinking a little critically about this!
1) Bob only needed to know that the siren was growing louder in order to make his deduction. A fire truck will use its siren while on the way to a fire, but has no need to sound it once it is returning to the station. Conversely, an ambulance must sound its siren when going either from the hospital to an emergency or returning from the site of the emergency to the hospital. Since the vehicle’s siren was growing louder, it was returning, and must have been an ambulance.
2) For this one, it is important that the two sirens sound the same (which is also true in the first riddle). However, Rupert does not know if the vehicle is coming or going, and he cannot see it, so there is no way for him to distinguish between the two vehicles. Still, knowing what each vehicle sounds like, Rupert would immediately recognize the sound of a third vehicle – one which produced a second, unique sound. That makes the answer the third common siren-producing vehicle in a city – a police car. Of course, for this answer to work, you have to assume that “a police car” is not a correct answer to the first riddle, and that’s somewhat silly.