A box-and-whisker plot drawn for the marks of 60 students shows least mark 18, lower quartile 32, median 45, upper quartile 58 and highest mark 74. About how many of the 60 marks lie between 32 and 58?

The box of a box-and-whisker plot runs from Q1 to Q3, and that stretch always holds the middle half of the data, so the count is 60 ÷ 2 = 30 marks. The number 26 is the LENGTH of the box, 58 − 32, which measures how spread out those marks are and not how many there are — the classic mix-up between a mark and a count. The value 15 is the quarter of the students lying below Q1, and 45 is the median mark.