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LDC1972
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Homework Statement
Showing all your working, calculate the arithmetic mean and standard deviation of the number of days lost.
Table shows man days lost to sickness..
Days lost: 1-3 4-6 7-9 10-12 13-15
Frequency 8 7 10 9 6
Homework Equations
n
They've given us this Ma = Ʃ = Xi / N
I=1
The Attempt at a Solution
The textbook they've supplied is really poor. They go into detail on all values centred around a single array. Obviously mine is a double...
So using Google and previous experience I've done this:
Taken medians of Days lost=
1-3 4-6 7-9 10-12 3-15
2 5 8 11 14 (medians)
median of frequency of days lost = 8 (central number as odd amount of numbers)
Multiplied median of days lost by frequency - (2x8) + (5x7) + (8x10) + 11x9) + (14x6) = 314
Summed frequency values 8 + 7 + 10 + 9 + 6 = 40 (Total frequency)
Divided 314/40 = 7.85 Arithmetic mean
Calculated variance
= median of days lost - Arithmetic mean
i.e 2 - 7.85 = 5.85 etc
Squared all results removing negative values to positive I.e -5.85^2 = 34.2225, did same for rest.
Multiplied squares by frequency i.e 34.2225 x 8 = 273.78 etc through the 5 values
Added all multiples 647.1
Divided multiples by 40 (the frequency) 64701/40 = 16.1775
Therefore σ2 = 16.1775 (The variance)
Calculated standard deviation by √16.1775 = 4.02212603
Basically if someone would be o kind as to confirm my approach and answers that'd be great But I don't expect anyone to spend hours on this!
Thanks for help if you can.
Lloyd
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