Answer:
mean height = 30.5
Explanation:
To find an estimate for the mean height, we need to use a pondered weight of the height of the plants.
The midpoints of each interval of height are:
0 to 10 -> 5
10 to 20 -> 15
20 to 30 -> 25
30 to 40 -> 35
40 to 50 -> 45
50 to 60 -> 55
Using the frequencies as the weights, we have:
mean height = (1*5 + 4*15 + 7*25 + 2*35 + 3*45 + 3*55) / (1+4+7+2+3+3)
mean height = 30.5