Jenny lives on Washington Street. About 8 to 11 cars pass by Jenny's house every 15 minutes. Which is a reasonable estimate for the number of cars that pass by Jenny's house in 120 minutes?

Answer 1

Take the average of 8 and 11 by adding them together and dividing by 2. (8+11)/2 = 19/2 = 9.5 That means an average of 9.5 cars pass her house in 15 minutes or 9.5/15 cars per minute 9.5/15 = 0.6333 cars per minute. Now multiply that rate by the number of total minutes - 120. 0.6333 * 120 = 76. So she would expect that an average of 76 cars would pass by her house in 120 minutes.

Another way to think about this is to figure out how many 15 minute intervals there are in 120 minutes. 120/15 = 8. That means there will be 8 intervals of 15 minutes during the 120 minutes. Each interval of 15 minutes will have 8 to 11 cars (or an average of 9.5 cars. Multiply 9.5 by 8 to get 76 cars