First, let’s break this down. What exactly are we looking at here? Well, Daisy measured the heights of 20 plants (in cm). The table, under Frequency, shows the # of plants that fit within a certain height range, shown on the left under Height of Plants (h).
Now, it says to take the midpoints of each group to figure out an estimate of the mean height. To find the mean, you add up all the totals and divide it by the # of items. So, let’s go through each row.
Midpoint of 0-10 is 5, and Frequency is 1, so that gives us 5. Midpoint of 10-20 is 15, Frequency is 4, and 15x4=60. We continue this with the other rows by finding the midpoint & multiplying the midpoint by the frequency (if the frequency is greater than 1). This gives us the numbers:
175 (25x7) 70 (35x2) 135 (45x3) 165 (55x3)
Now, we add these all together. 5+60+175+70+135+165=610
Finally, we divide 610 by the # of items (remember, there are 20 plants so we divide by 20) and 610/20 is 30.5.
FINAL ANSWER:
Thus, if I calculated correctly (which I hope I did lol), our estimate for the mean height of a plant is 30.5 cm!
