Hints and solutions to
Problem of the day for Friday, February 21

A crowd watching a parade fills the sidewalks on both sides of the street for a distance of 2 miles. The sidewalks are 10 feet deep and an average person needs 4 square feet to stand on. Which of the following is the best estimate for the number of people in the crowd:

  • (a) 25,000 people
  • (b) 50,000 people
  • (c) 100,000 people
  • (d) 250,00 people
  • (e) 500,000 people

(The picture above is of the Democratic Party parade in 1880.)


  • We'll assume the people use the space as efficiently as possible. So we need to figure out how many square feet of sidewalk there are.
  • Since the street is 2 miles long, the sidewalk on each side is roughly a rectangle with width 10 feet and length 2 miles (or 10,560 feet).
  • So the total area on both sides of the street is 2 x 10 x 10,560, or 211,200 square feet. (Given that we're estimating pretty roughly here, it's enough to say a little over 200,000 square feet).
  • Since each person needs 4 square feet to stand, we divide 200,000 by 4 to get around 50,000 people, so the answer is (b).