Rishi and Daisy take the same seven tests in Mathematics, and both students’ marks improve on successive tests. Their percentage marks are as follows.

Rishi’s marks ................................. Daisy’s marks
15 24 28 33 39 42 50 51 ............ 65 69 72 78 83 86

a. Explain why it would not be useful to use the range or the interquartile range alone as measures for comparing the marks of the two students.

b. Name two measures that could be used together to give a meaningful comparison of the two students’ marks.