Edexcel S1 2016 January — Question 6 9 marks

Exam BoardEdexcel
ModuleS1 (Statistics 1)
Year2016
SessionJanuary
Marks9
PaperDownload PDF ↗
Mark schemeDownload PDF ↗
TopicMeasures of Location and Spread
TypeAdding data values
DifficultyModerate -0.8 This is a straightforward S1 statistics question testing standard formulas and basic conceptual understanding. Part (a) requires direct application of mean and standard deviation formulas, (b) tests recall of skewness rules, while (c) and (d) require simple reasoning about how adding data affects summary statistics—all routine exercises with no problem-solving or novel insight required.
Spec2.02f Measures of average and spread2.02g Calculate mean and standard deviation2.02h Recognize outliers

6. Yujie is investigating the weights of 10 young rabbits. She records the weight, \(x\) grams, of each rabbit and the results are summarised below. $$\sum x = 8360 \quad \text { and } \quad \sum ( x - \bar { x } ) ^ { 2 } = 63840$$
  1. Calculate the mean and the standard deviation of the weights of these rabbits. Given that the median weight of these rabbits is 815 grams,
  2. describe, giving a reason, the skewness of these data. Two more rabbits weighing 776 grams and 896 grams are added to make a group of 12 rabbits.
  3. State, giving a reason, how the inclusion of these two rabbits would affect the mean.
  4. By considering the change in \(\sum ( x - \bar { x } ) ^ { 2 }\), state what effect the inclusion of these two rabbits would have on the standard deviation.
    END

Question 6:
Part (a)
AnswerMarks Guidance
\(\mu\) or \(\bar{x} = \frac{8360}{10} = 836\)B1
\(\sigma = \sqrt{\frac{\sum(x-\bar{x})^2}{10}} = \sqrt{6384}\) or \(4\sqrt{399} = 79.89993...\) = awrt \(79.9\)M1, A1 (3) M1 for \(\frac{63840}{10}\) with or without \(\sqrt{}\). NB \(\sum x^2 = 7052800\) but must see \(\sigma^2 = \frac{7052800}{10} - (836)^2\) for M1. A1 for awrt 79.9; accept \(s =\) awrt 84.2. Correct answer only M1A1
Part (b)
AnswerMarks Guidance
mean \(>\) median so positive skewB1 For correct comparison of mean and median (allow just \(836 > 815\))
dB1 (2)Dependent on 1st B1 for positive (skew) only. If mean \(< 815\) award B0B1 for comparison and statement of negative skew
Part (c)
AnswerMarks Guidance
\(\frac{776 + 896}{2} = 836\) which is same as \(\bar{x}\), or one is 60 above \(\bar{x}\), one 60 belowB1 For suitable calculation showing mean of two rabbits (or all 12) is same
So no change in the meandB1 (2) Dependent on suitable calculation or reason. If they only say differences are same (but not 1 above and 1 below) and state no change then B0B1
Part (d)
AnswerMarks Guidance
\((896 - 836)^2 = (776 - 836)^2 = 60^2 = 3600 < 6384\) the average of \(\sum(x-\bar{x})^2\)B1 For suitable calculation showing 60 or 3600 and comparing with 79.9 or 6384 respectively
Or \(\sum(x-\bar{x})^2 \to 63840 + 2 \times 60^2 = 71040\) and \(\frac{71040}{12} = 5920 < \frac{63840}{10}\)
So standard deviation will reducedB1 (2) Dependent on 1st B1 for stating s.d. "reduces"
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## Question 6:

### Part (a)
| $\mu$ or $\bar{x} = \frac{8360}{10} = 836$ | B1 | |
| $\sigma = \sqrt{\frac{\sum(x-\bar{x})^2}{10}} = \sqrt{6384}$ or $4\sqrt{399} = 79.89993...$ = awrt $79.9$ | M1, A1 (3) | M1 for $\frac{63840}{10}$ with or without $\sqrt{}$. NB $\sum x^2 = 7052800$ but must see $\sigma^2 = \frac{7052800}{10} - (836)^2$ for M1. A1 for awrt 79.9; accept $s =$ awrt 84.2. Correct answer only M1A1 |

### Part (b)
| mean $>$ median so positive skew | B1 | For correct comparison of mean and median (allow just $836 > 815$) |
| | dB1 (2) | Dependent on 1st B1 for positive (skew) only. If mean $< 815$ award B0B1 for comparison and statement of negative skew |

### Part (c)
| $\frac{776 + 896}{2} = 836$ which is same as $\bar{x}$, or one is 60 above $\bar{x}$, one 60 below | B1 | For suitable calculation showing mean of two rabbits (or all 12) is same |
| So no change in the mean | dB1 (2) | Dependent on suitable calculation or reason. If they only say differences are same (but not 1 above and 1 below) and state no change then B0B1 |

### Part (d)
| $(896 - 836)^2 = (776 - 836)^2 = 60^2 = 3600 < 6384$ the average of $\sum(x-\bar{x})^2$ | B1 | For suitable calculation showing 60 or 3600 and comparing with 79.9 or 6384 respectively |
| Or $\sum(x-\bar{x})^2 \to 63840 + 2 \times 60^2 = 71040$ and $\frac{71040}{12} = 5920 < \frac{63840}{10}$ | | |
| So standard deviation will reduce | dB1 (2) | Dependent on 1st B1 for stating s.d. "reduces" |

The image appears to be essentially blank/empty — it only contains the "PMT" header in the top right corner and the Pearson Education Limited copyright footer at the bottom. There is no mark scheme content visible on this page to extract.

This appears to be a blank back page of a Pearson/Edexcel mark scheme document. Could you share the pages that actually contain the mark scheme questions and answers?
6. Yujie is investigating the weights of 10 young rabbits. She records the weight, $x$ grams, of each rabbit and the results are summarised below.

$$\sum x = 8360 \quad \text { and } \quad \sum ( x - \bar { x } ) ^ { 2 } = 63840$$
\begin{enumerate}[label=(\alph*)]
\item Calculate the mean and the standard deviation of the weights of these rabbits.

Given that the median weight of these rabbits is 815 grams,
\item describe, giving a reason, the skewness of these data.

Two more rabbits weighing 776 grams and 896 grams are added to make a group of 12 rabbits.
\item State, giving a reason, how the inclusion of these two rabbits would affect the mean.
\item By considering the change in $\sum ( x - \bar { x } ) ^ { 2 }$, state what effect the inclusion of these two rabbits would have on the standard deviation.

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\hfill \mbox{\textit{Edexcel S1 2016 Q6 [9]}}