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Mars2501 [29]
4 years ago
7

PLEASE ANSWER QUICKLY ASAP ANSWER QUESTION A AND B​

Mathematics
1 answer:
Evgen [1.6K]4 years ago
4 0

Answer:

a) a+b+c=\begin{pmatrix}-2\\-3\end{pmatrix}

b) (i) a+2c=\begin{pmatrix}-4\\2\end{pmatrix}

   (ii) k=2

Step-by-step explanation:

It is given that,

a=\begin{pmatrix}4\\-10\end{pmatrix},b=\begin{pmatrix}-2\\1\end{pmatrix},c=\begin{pmatrix}-4\\6\end{pmatrix}

a)

We need to find the value of a+b+c.

a+b+c=\begin{pmatrix}4\\-10\end{pmatrix}+\begin{pmatrix}-2\\1\end{pmatrix}+\begin{pmatrix}-4\\6\end{pmatrix}

a+b+c=\begin{pmatrix}4+(-2)+(-4)\\-10+1+6\end{pmatrix}

a+b+c=\begin{pmatrix}-2\\-3\end{pmatrix}

b)

(i) We need to find the value of a+2c.

a+2c=\begin{pmatrix}4\\-10\end{pmatrix}+2\begin{pmatrix}-4\\6\end{pmatrix}

a+2c=\begin{pmatrix}4\\-10\end{pmatrix}+\begin{pmatrix}-8\\12\end{pmatrix}

a+2c=\begin{pmatrix}4+(-8)\\-10+12\end{pmatrix}

a+2c=\begin{pmatrix}-4\\2\end{pmatrix}

(ii) It is given that a+2c=kb, where k is an integer. We need to find the value of k.

a+2c=k\begin{pmatrix}-2\\1\end{pmatrix}

\begin{pmatrix}-4\\2\end{pmatrix}=\begin{pmatrix}-2k\\k\end{pmatrix}

On comparing both sides, we get

k=2

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<h3>Answer:    1  question left blank</h3>

He answered 16 questions correctly, and got 3 wrong answers.

==========================================================

Explanation:

Let

  • x = number of questions that are correct
  • y = number of wrong answers
  • z = number of questions left blank

x,y,z are nonnegative whole numbers.

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Since there are 20 questions total, this means the first equation to set up is:

x+y+z = 20

Solving for y leads to

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Another equation to set up is 7x-4y = 100 because Eric earns 7 points per correct answer and loses 4 points for each incorrect answer, and all that leads to 100 points total which was his quiz score. We'll ignore the questions he left blank since they add 0 points.

Let's plug the equation in which we isolated y

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Now we can guess and check to see which pair of x and z values will make that last equation above true. I suggest starting with the smallest possible value of x and using that x value to solve for z.

If x = 0, then,

11x+4z = 180

11(0)+4z = 180

4z = 180

z = 180/4

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So if Eric got 0 correct answers, then he left 45 questions blank. But that isn't possible because there are only 20 questions total. So we'll ignore the case that x = 0.

If we increase x by 4, and decrease z by 11, then we get another ordered pair solution to this equation

So another solution is (x,z) = (4,34)

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But like before, z = 34 isn't possible since 20 is the max.

Increase x by 4 again, and drop z by 11 to get (x,z) = (8,23). Again we run into the same issue as before.

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Do another round of "increase x by 4, decrease z by 11" to get to (x,z) = (16, 1). This is the only case left because anything beyond this, z will be negative.

Luckily, this final case does work. If Eric answers x = 16 questions correctly, then he left z = 1 of them blank. That must mean y = 20-x-z = 20-16-1 = 3 questions were incorrect.

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-------------------

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