Statistics II

No calculator

Try each one on paper first, then check a single step. That is worth far more than reading a finished solution.

Example 1 — estimating the mean of grouped data

Forty students sat a test. Marks 1–10: 4 students; 11–20: 7; 21–30: 12; 31–40: 9; 41–50: 8. Estimate the mean mark.

Find the median, the quartiles and the interquartile range of $3, 5, 7, 8, 10, 12, 15, 18$ .

A bag holds 4 red, 3 blue and 5 green marbles. One is drawn at random. Find $P(\text{blue})$ and $P(\text{not green})$ .