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1. 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

Solution:

Let the number be x
Then,

\begin{aligned} \Leftrightarrow 3 x^{2} - 4 x = x + 50 \\ \Leftrightarrow 3 x^{2} - 5 x - 50 = 0 \\ \Leftrightarrow (3 x + 10) (x - 5) = 0 \\ \Leftrightarrow x = 5 \end{aligned}

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