in a quiz competition a student answers n quest... - WAEC Mathematics 2011 Question
in a quiz competition, a student answers n questions correctly and was given D(n + 50) for each question correctly answered. If he gets D600.00 altogether, how many questions did he answer correctly?
A
18
B
15
C
12
D
10
correct option: d
let the number of question = n
n(n + 50) = 600
n2 + 50n - 600 - 0 by quadratic formular
x = \(\frac{b \pm \sqrt{b^2 - 4ac}}{2}\)
n = \(\frac{-50 \pm \sqrt{50^2 - 4(1) (-600)}}{2(1)}\)
= \(\frac{-50 \pm \sqrt{4900}}{2}\)
= \(\frac{-50 + 70}{2}\)
= \(\frac{20}{2}\)
= 10
n(n + 50) = 600
n2 + 50n - 600 - 0 by quadratic formular
x = \(\frac{b \pm \sqrt{b^2 - 4ac}}{2}\)
n = \(\frac{-50 \pm \sqrt{50^2 - 4(1) (-600)}}{2(1)}\)
= \(\frac{-50 \pm \sqrt{4900}}{2}\)
= \(\frac{-50 + 70}{2}\)
= \(\frac{20}{2}\)
= 10
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