2025 SST PRELIMS P1 Q20

The cumulative frequency curve shows the depths, \(d\) mm, of a canal measured daily for 200 days.

1. Use the curve to estimate
   1. the median depth,[1]
   2. the interquartile range,[1]
   3. the depth at the 30th percentile,[1]
   4. the number of days when the depth was at least 450 mm.[1]
2. The grouped information is shown below.
   1. Find \(m\) and \(n\).[1]
   2. Calculate an estimate of the mean depth.[1]

   Depth (mm)	\(100<d\leq200\)	\(200<d\leq300\)	\(300<d\leq400\)	\(400<d\leq500\)
   No. of days	\(12\)	\(m\)	\(n\)	\(100\)