Question

FOR 14 POINTS Thalia, a quiz show contestant, answered 20 questions. She was awarded 2 points for every correct answer that she gave, but she was penalized 1 point for every incorrect answer. In the end, Thalia had a total of 28 points. In order to determine the number of correct and incorrect answers that she gave, a viewer at home used the system of linear equations x + y = 20 and 2 x + y = 28, with x being the number of correct answers and y being the number of incorrect answers. The viewer solved the system by using the linear combination method as shown. x + y = 20. + StartFraction Negative 2 x minus y = negative 28 over Negative x = negative 8 EndFraction. StartFraction negative x Over negative 1 EndFraction = StartFraction negative 8 Over negative 1 EndFraction. X = 8. 8 + y = 20. 8 + y minus 8 = 20 minus 8. y = 12. The viewer calculated that the contestant answered 8 questions correctly and 12 questions incorrectly. What went wrong? The viewer mistakenly determined that one of the equations in the system should be x + y = 20.Instead modifications should have been made before applying the equation. The viewer mistakenly determined that one of the equations in the system should be 2 x + y = 28. Instead modifications should have been made before applying the equation. The viewer multiplied the equation 2 x + y = 28 by –1 incorrectly. The viewer added the equations x + y = 20 and Negative 2 x minus y = negative 28 incorrectly.

Answer 1

Answer:

The viewer mistakenly determined that one of the equations in the system should be 2 x + y = 28. Instead modifications should have been made before applying the equation.

Step-by-step explanation:

Given

Total Questions = 20

Total Points = 28

Correct Answers = +2 points

Incorrect Answers = -1 point

Required

Spot the error in the viewer's calculation

The viewer represents the correct answers with x and the incorrect ones with y.

This implies that

$x + y = 20$

Also, for every correct answers, she gets 2 points;

This can be represented by 2x

and for every incorrect answers, she gets -1 point

This can be represented by -y

This implies that

$2x - y = 28$

This is where the viewer made a mistake

The viewer's mistake is that; instead of subtracting total incorrect points from the correct points, the viewer added them together;

Solving further

$2x - y = 28$

$x + y = 20$

Add both equations together

$2x + x + y - y = 28 + 20$

$3x = 48$

Divide both sides by 3

$\frac{3x}{3} = \frac{48}{3}$

$x = \frac{48}{3}$

$x = 16$

Substitute $x = 16$ in $x + y = 20$

$16 + y = 20$

Subtract 16 from both sides

$16 - 16 + y = 20 - 16$

$y = 20 - 16$

$y = 4$

This implies that the contestant answered 16 questions correctly and 4 questions incorrectly

Answer 2

Answer: A

Step-by-step explanation: