Question

in an exam one mark is awarded for correct answer and 1/2 mark is detected for every wrong answer. Jaya answered 120 questions and secured 90 marks. how many questions did she answer correctly

Answer 1

let correct answer be x and wrong answer be y
the
x+y=120
x+0.5y=90
subtracting we get
1.5y=30
y=20
correct answer=100

Answer 2

The Calculation for this question is as follows;

Let the number of questions answered correctly be x
And the number of questions answered incorrectly be y

Total number of questions:

= total number of correct answers + total number of incorrect answers = 120 questions
That means,  x + y = 120    .....first equation

Marks scored;

For correct answers is 1 mark × x answers = X marks
For incorrect answers  -1/2 mark × y answers = -0.5Y marks

Therefore,   x +(-  0.5y) = 90 marks
                  =  x - 0.5y = 90   (second equation)

We now have two equations and can thus solve the problem:

x + y = 120     (x = 120-y)
x - 0.5y = 90

Substitute x = 120 - y in the second equation

120 -y - 0.5y = 90
-1.5y = 90 -120
-1.5y = - 30
1.5y = 30
y = 20

...find x

x = 120 - y
x = 120 - 20
x= 100

x is the number of correctly answered questions

Therefore the number correctly answered questions = 100 questions