Question

Thrice the square of a natural number decreased by $4$ times the number is equal to $50$ more than the number. The number is

• A. $4$
• B. $5$
• C. $6$
• D. $10$

Answer 1

The correct option is B $5$

Let the natural number be $x$.

Then according to the given condition,
$3x^2-4x=50+x$
$3x^2-5x-50=0$
$3x^2-15x+10x-50=0$
$3x(x-5)+10(x-5)=0$
$(3x+10)(x-5)=0$

$\therefore x=\frac{-10}{3}$ and $x=5$.

Since, x is given to be a natural number, so x = 5.