The table below shows a multiple-choice test Sam and Roger took.

  1. (a)

    Represent this information in a 2×32\times3 matrix, S.

    Answer S=(  )S=\left(\ \ \right)

  2. (b)

    The marks are awarded as follows:

    Correct = 2 marks

    No attempt = 0 mark

    Incorrect = -1 mark

    Represent the information in a 3×13\times1 matrix, T.

    Evaluate STST

  3. (c)

    Explain what your answer to (b) represents.

    Answer ...

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Worked solution

8(a)

1. Arrange the table values into a $2\times3$ matrix in the given order.

Rows: Sam, Roger.
Columns: Correct, No attempt, Incorrect.

S=(14511505)S=\begin{pmatrix}14&5&1\\15&0&5\end{pmatrix}

Answer

S=(14511505)S=\begin{pmatrix}14&5&1\\15&0&5\end{pmatrix}

8(b)

1. Represent the marks awarded as a $3\times1$ matrix in the correct order.

Since the columns of SS are in the order Correct, No attempt, Incorrect,
T=(20−1)T=\begin{pmatrix}2\\0\\-1\end{pmatrix}

2. Multiply $S$ by $T$ to find the total marks for each contestant.

Using S=(14511505),S=\begin{pmatrix}14&5&1\\15&0&5\end{pmatrix},
ST=(14511505)(20−1)ST=\begin{pmatrix}14&5&1\\15&0&5\end{pmatrix}\begin{pmatrix}2\\0\\-1\end{pmatrix}
=(14(2)+5(0)+1(−1)15(2)+0(0)+5(−1))=\begin{pmatrix}14(2)+5(0)+1(-1)\\15(2)+0(0)+5(-1)\end{pmatrix}
=(2725)=\begin{pmatrix}27\\25\end{pmatrix}

Answer

T=(20−1),ST=(2725)T=\begin{pmatrix}2\\0\\-1\end{pmatrix},\qquad ST=\begin{pmatrix}27\\25\end{pmatrix}

8(c)

1. State what the product matrix $ST$ means in the context of the test scores.

From part (b),
ST=(2725).ST=\begin{pmatrix}27\\25\end{pmatrix}.
The first row corresponds to Sam and the second row corresponds to Roger. Hence the values are their total marks in the test.

Answer

The entries of STST represent the total marks scored by Sam and Roger respectively. Sam scored 2727 marks and Roger scored 2525 marks.

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