CAIE S1 2002 June — Question 5 8 marks

Exam BoardCAIE
ModuleS1 (Statistics 1)
Year2002
SessionJune
Marks8
PaperDownload PDF ↗
Mark schemeDownload PDF ↗
TopicPermutations & Arrangements
TypeBasic arrangements with repeated letters
DifficultyModerate -0.3 This is a standard permutations question with repeated elements (two 2s). Part (i) is direct application of the formula for permutations with repetition. Parts (ii) and (iii) require treating groups as single units and case-work for even endings respectively, but these are textbook techniques covered in S1. The question is slightly easier than average A-level due to being routine application of standard methods with no novel insight required.
Spec5.01a Permutations and combinations: evaluate probabilities

The digits of the number 1223678 can be rearranged to give many different 7-digit numbers. Find how many different 7-digit numbers can be made if
  1. there are no restrictions on the order of the digits, [2]
  2. the digits 1, 3, 7 (in any order) are next to each other, [3]
  3. these 7-digit numbers are even. [3]

AnswerMarks Guidance
(i) \(\frac{7!}{2!} = 2520\)M1, A1 2 For dividing by 2 or 2!; For correct answer
(ii) \(\frac{5!}{2!} \times 3! = 360\)B1, M1 For 5! or equivalent; For multiplying by 3! or dividing by 2! or both
A1 3For correct answer
(iii) \(\frac{4}{7} \text{ of } 2520 = 1440\)M2, A1 For 4/7 of their (i); For correct answer
OR \(6! \cdot \frac{6}{2} \cdot \frac{6}{2} = 1440\)M1, A1, A1 3 For summing options for ending in 2, 6, 8; For correct options; For correct answer
(ii) (i) \(\mu = 3.6\)B1 Stated or can be calculated later on
\(\frac{2.8 - (\text{their}\mu)}{\sigma} = -0.4\)M1 For equation relating \(\mu\) or 3.6 and \(\sigma\). Must be standardised, can have ±0.4
\(\sigma = 2\)M1 Solving the correct equation or with a second correct equation relating \(\mu\) and \(\sigma\)
A1 4For correct answer
**\((0.6554)^4 \times (0.3446)^3 \times _4C_3 + (0.6554)^3 \times (0.3446)^4 \times _4C_3 = 0.879\) (= 0.3061 +0.3881 +0.1845)M1, B1, A1, A1 For attempted binomial calculation of any 2 or 3 of P(2), P(3), P(4), needs 0.6554 in; For correct numerical expression for P(2) or P(3); All in correct form; For correct answer
OR \(1 - (0.3446)^4 - (0.6554)^4 \times (0.3446)^3 \times _4C_3 (= 1 - 0.0141 - 0.1072) = 0.879\)M1, B1, A1, A1 4 For calculation of 1 – any 2 or 3 of P(0), P(1), P(2); For correct numerical expression for P(1) or P(2); All in correct form; For correct answer
**(i)** $\frac{7!}{2!} = 2520$ | M1, A1 2 | For dividing by 2 or 2!; For correct answer

**(ii)** $\frac{5!}{2!} \times 3! = 360$ | B1, M1 | For 5! or equivalent; For multiplying by 3! or dividing by 2! or both

| A1 3 | For correct answer

**(iii)** $\frac{4}{7} \text{ of } 2520 = 1440$ | M2, A1 | For 4/7 of their (i); For correct answer

OR $6! \cdot \frac{6}{2} \cdot \frac{6}{2} = 1440$ | M1, A1, A1 3 | For summing options for ending in 2, 6, 8; For correct options; For correct answer

**(ii) (i)** $\mu = 3.6$ | B1 | Stated or can be calculated later on

$\frac{2.8 - (\text{their}\mu)}{\sigma} = -0.4$ | M1 | For equation relating $\mu$ or 3.6 and $\sigma$. Must be standardised, can have ±0.4

$\sigma = 2$ | M1 | Solving the correct equation or with a second correct equation relating $\mu$ and $\sigma$

| A1 4 | For correct answer

**$(0.6554)^4 \times (0.3446)^3 \times _4C_3 + (0.6554)^3 \times (0.3446)^4 \times _4C_3 = 0.879$ (= 0.3061 +0.3881 +0.1845) | M1, B1, A1, A1 | For attempted binomial calculation of any 2 or 3 of P(2), P(3), P(4), needs 0.6554 in; For correct numerical expression for P(2) or P(3); All in correct form; For correct answer

OR $1 - (0.3446)^4 - (0.6554)^4 \times (0.3446)^3 \times _4C_3 (= 1 - 0.0141 - 0.1072) = 0.879$ | M1, B1, A1, A1 4 | For calculation of 1 – any 2 or 3 of P(0), P(1), P(2); For correct numerical expression for P(1) or P(2); All in correct form; For correct answer
The digits of the number 1223678 can be rearranged to give many different 7-digit numbers. Find how many different 7-digit numbers can be made if

\begin{enumerate}[label=(\roman*)]
\item there are no restrictions on the order of the digits, [2]
\item the digits 1, 3, 7 (in any order) are next to each other, [3]
\item these 7-digit numbers are even. [3]
\end{enumerate}

\hfill \mbox{\textit{CAIE S1 2002 Q5 [8]}}