10 The table gives information about the heights of 50 trees. Height (h metres) Frequency 0 < h - 4 ,8, 4 < h - 8 ,21, 8 < h - 12, 12, 12 < h - 16, 7, 16 < h - 20, 2. Work out an estimate for the mean height of the trees.

First find the appropriate mid points of each set of intervals. These will be 2, 6, 10, 14 and 18, and you get these my dividing in two the interval range. Then multiply each midpoint by the corresponding frequency and sum each one. Therefore: (2x8) + (6x21) + (10x12) + (14x7) + (18x2). The sum total should be 396. You then have to divide by the total frequency for the estimate of the mean, the final answer is then 7.92.