# S1Ch3 – Measures of Dispersion – 11.12.15

Hi all,

Sorry that it has been a while between posts this time!

Firstly, a quick summary of you Ch1 and Ch2 assessments:

Ch1 was generally completed to a very high standard, with no one losing marks for incorrect answers. However, an awful lot of you lost marks simply because you didn’t see Q1a – please make sure that this never happens again!!!

In chapter 2, the questions on calculating the mean were done well, and lots of you had a good attempt at linear interpolation. Most common mistakes were:

• Q1, where the class boundaries were, e.g. 0.0-1.0, 1.0-2.0, people used 0.5 as the lower class boundary for the second class – we discussed this in lesson today and hopefully you are a bit clearer with this now
• Q4a – probability. remember to find the probability of two independent events you multiply the probabilities together, lots of you misread this question and just wrote a single probability.
• Miscounting the cumulative frequency column – again, a really silly mistake that I hope isn’t repeated ðŸ™‚

This lesson was a consolidation lesson, focussing on using interpolation to answer questions about quartiles and percentiles.

Remember, for quartiles,Â  the first question that we ask ourselves is, is the data continuous or discrete? If it is continuous we use n/4 and 3n/4 and then use interpolation. if it is discrete we use n/4 and 3n/4 – if it is a whole number we look for the term halfway between that one andÂ  the one above (e.g. if it comes out as 25, we look for the value of the 25.5th piece of data). If it is a decimal we round up (regardless of the number) and pick corresponding term.

We use a similar system for percentiles; to calculate the xth percentile, Px, we find the value of the xn/100th term.

Homework this week is to ensure that Ex3A (odd questions) and Ex3B (Q2-5) are completed and marked. For extra practice, read through these notes and try the questions: S1 Ch3 Notes and Examples.

Nest lesson we will finish looking at Standard Deviation (which we started last week so that you were ready for Mrs Price’s work) on Tuesday (if you are at choir rehearsals that day be sure to catch up any work missed), and on Friday we will look how coding affects the standard deviation. Your Christmas holiday work will simply be to complete the Mixed Exercise, and then we can go over anything that you’re unsure with, before setting the assessment in the first week back.

Thanks for reading – have a lovely weekend ðŸ™‚

Mrs Shaw

# Statistics Update

Hi all,

Just a quick post this time (I’ll do a full post after next lesson when there’s a bit more to talk about!), sharing a resource which will be useful over the next few weeks of S1…

This file shows you how to calculate various things (e.g. variance, PMCC) using a Casio Calculator – if you’ve some free time it would be worth investigating this further.

Don’t forget, lots of homework due for Tuesday:

• Ex2F (Mixed Exercise)
• S1Ch1 assessment
• S1Ch2 assessment.

Hope you’ve had a nice weekend,

Mrs Shaw

# Averages from Grouped Frequency Tables 1/12/15

Hi all,

Today we finished off S1Ch2, covering finding averages from grouped frequency tables. The main difference between GCSE and A Level for this topic is finding the median – we now use linear interpolation, instead of just saying which class the median is. Please watch this video if you weren’t in/need extra help. You need to be able to do this confidently to allow you to progress onto S1Ch3 successfully. See page 13-15 of Â thisÂ document for extra examples. In class you completed Ex2D.

Your homework (due a week today – 8th December) was to complete:

• Mixed Exercise 2F
• S1Ch1 assessment
• S1Ch2 assessment.

Remember to make the most of P6! If you get stuck, comment below and someone can help you.

See you on Friday,

Mrs Shaw