Final answer:
The average speed of the plane around the field is 221 km/h. Option D is correct.
Step-by-step explanation:
To find the average speed of the plane around the field, we need to calculate the total distance traveled and divide it by the total time taken. The plane flies along the four sides of a square, so the distance traveled is equal to the perimeter of the square.
The perimeter of a square is found by multiplying the length of one side by 4. In this case, the sides of the square represent the distances traveled at different speeds. So the total distance is calculated by adding the four speeds: 100 + 200 + 300 + 400 = 1000 km.
The total time taken is the sum of the time taken to travel each side of the square. We can calculate the time by dividing the distance traveled by the speed: 100/100 + 200/200 + 300/300 + 400/400 = 1 + 1 + 1 + 1 = 4 hours.
Now we can calculate the average speed by dividing the total distance by the total time: 1000 km / 4 hours = 221 km/h.