JAMB 1991 · UME · Q22

Find the positive number $n$ such that three times its square is equal to twelve times the number.

Worked solution (try it first)

Write the sentence as an equation: $3n^2 = 12n$ .
Bring everything to one side and factorise: $3n(n - 4) = 0$ , so $n = 0$ or $n = 4$ .
The number is positive, so $n = 4$ , option D.