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Consider the following inequalities.

(i) \(3p - q \lt 4\)
(ii) \(3q - p \lt 12\)

Which one of the following expressions below satisfies the above two inequalities?

  • A.\(p + q \lt 8\)
  • B.\(p + q = 8\)
  • C.\(8 \le p + q \lt 16\)
  • D.\(p + q \ge 16\)

Answer: A

The expression that follows is \(p + q \lt 8\).

Add the two inequalities, which is allowed because both point the same way:

\[ \begin{aligned} (3p - q) + (3q - p) &\lt 4 + 12 \\ 2p + 2q &\lt 16 \\ p + q &\lt 8 \end{aligned} \]

So every pair \((p, q)\) satisfying both inequalities has \(p + q\) strictly less than 8. The other options all allow \(p + q \ge 8\), which the sum rules out: \(p + q = 8\) would need \(2(p + q) = 16\), but the sum must be strictly less than 16.

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