Paper 1 · Sequences and Series

From $\dfrac{nx(n+19)}{20}>100x$ , cancel $x$ and simplify to a quadratic inequality in $n$ , in the form $n^2+bn+c>0$ .

Model answer

n^2+19n-2000>0

Also accepted: n^2 + 19n - 2000 > 0

Explanation: Cancelling

x

:

n(n+19)>2000

, i.e.

n^2+19n-2000>0

.

Derived from ZIMSEC Mathematics Paper 1, June 2011, Q12

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