The area of the field is 100 square meters. Each 1-meterby-1-meter square has an area of 1 square meter.
Thus, on average, the earthworm counts to a depth of 5 centimeters for each of the regions investigated by the students should be about
of the total number of earthworms to a depth of 5 centimeters in the entire field.
Since the counts for the smaller regions are from 107 to 176, the estimate for the entire field should be between 10,700 and 17,600.
Therefore, of the given choices, 15,000 is a reasonable estimate for the number of earthworms to a depth of 5 centimeters in the entire field.
Choice A is incorrect; 150 is the approximate number of earthworms in 1 square meter.
Choice B is incorrect; it results from using 10 square meters as the area of the field.
Choice D is incorrect; it results from using 1,000 square meters as the area of the field.