CAIE S1 2005 June — Question 2

Exam BoardCAIE
ModuleS1 (Statistics 1)
Year2005
SessionJune
TopicMeasures of Location and Spread
TypeCalculate mean from coded sums
2 The following table shows the results of a survey to find the average daily time, in minutes, that a group of schoolchildren spent in internet chat rooms.
Time per day
\(( t\) minutes \()\)
Frequency
\(0 \leqslant t < 10\)2
\(10 \leqslant t < 20\)\(f\)
\(20 \leqslant t < 40\)11
\(40 \leqslant t < 80\)4
The mean time was calculated to be 27.5 minutes.
  1. Form an equation involving \(f\) and hence show that the total number of children in the survey was 26 .
  2. Find the standard deviation of these times.
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