Age of Surface Puzzle Answers:
     Consider that for a particular period of time, the number of nearby asteroids (and other conditions) are such that the number of impact craters on a planet is about 1 every 1000 years for a region the size of region A or region B below.

1)  About how long has it been since region B was resurfaced?
     Since there are 7 craters in this region, and craters form on average about once every 1000 years, this region was resurfaced about 7000 years ago.

2)  How old is region A?
      Since there are 19 craters, and craters form about every 1000 years, this area is about 19000 years old.

3)  How old is the planet these regions are found on?
      Since both of these regions could have been resurfaced many times, erasing previous craters, there is no way to tell from this how old the planet is.

4)  In which case is the relative uncertainty of the age the greatest, for region A or region B?
     Because there are fewer craters in region B (reflecting its younger age), their is greater relative uncertainty in its age.  This is analogous to flipping a coin:  50% of the time the coin will come down tails, on average.  BUT, if you flip the coin only twice, there is a good chance that you won't get one heads and one tails (the average).  But if you flip the coin many times, the result will be very close to 50% heads and 50% tails.  The relative uncertainty decreases with increasing number of flips.  Likewise, the relative uncertainty of the age decreases with increasing number of craters.

 
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