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# Statistics HELP :( watch

1. Hi there, my teacher went through this question in class, i didn't get a single thing. Please help!

b) The company fits a standby battery to its power supplies and has recently been experiencing problems with its life. The battery supplier claims that it should last for 200 hours under normal conditions as their tests show a mean life of 200 hours. The designer of the power supply is not convinced. A technician has tested 220 batteries for you and tabulated the results. The designer asks you to process them and to establish what the working life really is. Here are the figures.
Life (hrs) Number
190—192 46
192—194 15
194—196 26
196—198 25
198—200 28
200—202 27
202—204 24
204—206 12
206—208 8
208—210 5
210— 212 4

Calculate the measures of central tendency and feed your thoughts to the designer.
2. You could estimate the mean and standard deviation or you could interpolate the median.

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3. is that all? it says calculate the central tendency.. and feed the thoughts.. what exactly do they want?
4. (Original post by SpikeSpiegel)
is that all? it says calculate the central tendency.. and feed the thoughts.. what exactly do they want?
mean and median are measures of central tendency
standard deviation and inter quartile range are measures of spread
once you have calculated one of them, or both, you can comment on the battery makers claims about the mean life.
5. ok ive calculated the measures of tendency.. which is mean and median! ... how do I comment on that?
6. (Original post by SpikeSpiegel)
ok ive calculated the measures of tendency.. which is mean and median! ... how do I comment on that?
How do they compare with the claims made by the battery maker?

I have not done the calculations but it looks like the data is skewed so the median life is less than the mean.
If that's the case then typical battery life is less than the mean the manufacturer claims

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7. (Original post by SpikeSpiegel)
what level is this work?
8. BTEC level 3
9. (Original post by SpikeSpiegel)
BTEC level 3
are you meant to use confidence intervals?
10. no?
11. (Original post by SpikeSpiegel)
no?
I do not know much about the level BTEC but

measures of central tendency are simply averages such as the mean and median

as data is grouped

then mean will be estimated by using the midpoints

the median will be estimated by a Cumulative frequency graphs or interpolation.

for video tutorials go to UTUBE and type

mean of grouped data
median of grouped data

Also look atPages 20 - 24 on the link

there some worked solution there.

hope these are useful
12. What was the mean? median?
13. Have you found the mean and median? How do they compare to the '200 hours' in the question?

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Updated: January 17, 2015
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