# Thread: Cambridge A Level Statistics : Exercise Problem :(

1. ## Cambridge A Level Statistics : Exercise Problem :(

Extract from "Statistics 1 - Steve Dobbs and Jane Miller (Cambridge University Press)"

I nearly work out the problem, class boundaries are all ok but two solutions from the book don't match with mine,
Hope I have understood the question as it should.
Below is my solution for you to check. Hope you will solve it right. thank.

11.4 - (12th highest salinity level)
3.3 % - ( percentage error in this estimate)

1.Question (Pg 21. Miscellaneous Exercise 1, Question 4)
click on Image :

2. My Work-out Solution
click on Image:

2. ## Re: Cambridge A Level Statistics : Exercise Problem :(

I manage to find the perfect match for the answer. Thank anyways - BUT still in CoNfUsIoN - is it from the BOOK or the MIND? !!!

The solution is very easy to reach, but the question is HARD to understand clearly, lacking precision maybe.

__________________________________________________ ____
My work-out solution on the graph above is WRONG: I divide 30/12 = 2.5 - infact it is referring to 12 th value not 12 divisions.

QUESTION IS: ESTIMATE THE 12TH HIGHEST SALINITY LEVEL.

so, What Should I understand by that?
1. The 12th highest value could simply be the 12th value of the first 12 values at the beginning of the distribution. ( 12 match with ≈ 10.3)
2. It could be just the highest value of the last top 12 highest values or the highest value of the distribution itself. (30 match with ≈ 15.95)
3. And less likely to be the least value of the last top 12 highest values or the first value of the last top 12 highest values of the distribution
(30 -12 = 18 match with ≈ 11.4 Book Given Answer :!)

Maybe the Question should be : ESTIMATE THE 18th HIGHEST SANITY LEVEL,
or could it be an error in the original question,
or that it is us who is mistaken?

In a hurry, one could have taken any one of these 2 first possibilities as answer, and less likely the 3rd one.

Hope someone else could give the last and best explanation here .

* I suggest you work out that simple statistics question on graph on your own and comment about the answer you get, thank again.

3. ## Re: Cambridge A Level Statistics : Exercise Problem :(

I had emailed a CIE officer regarding this thread a long time ago and kindly of him he replied back but I forgot to put it here, so here I go:

Dear Customer,

Thank you for your enquiry. I've had a quick look at the question in the book and your thread, and I can see where the confusion may lie.

The question asks for an estimate of the 12th highest salinity level. The highest salinity level would clearly be 15.95 from the cumulative frequency graph. Now you must work backwards from this to find the 12th highest level which lies at approx 11.4. This would indeed be the 18th from the lowest salinity level (as you have indicated in your 3rd answer possibility).

It seems that this is mainly an interpretation issue - you clearly understand the main mathematical principles in this question.

Enjoy working through the rest of the book.

Best wishes,

Ashley