Stage 9 - Q7 - 5 marks
20233
The midpoint estimate of the mean is exactly 30 minutes. Find the missing frequency in the table.
Time (min)
Frequency
\(10\le t<20\)
3
\(20\le t<30\)
?
\(30\le t<40\)
18
Hint
The unknown frequency changes the total number of observations as well as the total midpoint products.