10th Class Mathematics Pair of Linear Equations in Two Variables Question Bank Case Based (MCQs) - Pair of Linear Equations in Two Variables

If answer to all questions be attempted by guessing were wrong, then how many questions answered correctly to score 90 marks?

A) 24

B) 70

C) 96

D) 100

Correct Answer: D

Solution :

Let number of questions be answered correctly be x.

Then, Number of questions be answered by giving \[=(120-x)\].

So. \[x\times 1+(120-x)\times \left( -\frac{1}{4} \right)=90\]

\[\Rightarrow \,\,\,\,\,\,\,\,\,\,4x-(120-x)=380\]

\[\Rightarrow \,\,\,\,\,\,\,\,\,\,5x=380+120=500\]

\[\Rightarrow \,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,x=100\]

Hence, he answered 100 answer correctly.

So option [d] is correct.