NIFT UG 2018 Question Paper with solutions

Question : 9 of 150

Marks: +1, -0

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

Solution:

Let the number be

x

According to the question,

3 × x^{2}-4 × x=x+50

⇒ \;\; 3 x^{2}-5 x-50=0

⇒ \;\; 3 x^{2}-15 x+10 x-50=0

⇒ \;\; 3 x(x-5)+10(x-5)=0

⇒ \;\; (x-5)(3 x+10)=0

⇒ \;\; x=5

\;{-10}/{3}

But the number is natural.

∴

Hence, required number

=5

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