Question

If Vivek will score $20$ more marks in his biology test out of $50$ marks, $10$ times of these marks will be the square of the actual marks, then the marks that he scored is

• A. $15$ marks
• B. $25$ marks
• C. $20$ marks
• D. $10$ marks

Answer 1

The correct option is C $20$ marks

Let the marks scored by Vivek in the test be $x$.
According to the question:
$(20+x)\times 10=x^2$
$\Rightarrow 200+10x=x^2$
$\Rightarrow x^2-10x-200=0$
$\Rightarrow x^2-20x+10x-200=0$
$\Rightarrow x(x-20)+10(x-20)=0$
$\Rightarrow (x-20)(x+10)=0$
$\Rightarrow x=20,-10$
Hence, the correct answer is option (3).