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Question

Consider the following inequalities.
(i) $3p - q < 4$ 
(ii) $3q - p < 12$ 
Which one of the following expressions below satisfies the above two inequalities?

The correct answer is
$p+q<8$

Analyzing the Inequalities

We are given two inequalities:

  • Inequality (i): $3p - q < 4$
  • Inequality (ii): $3q - p < 12$

We need to find an expression for $p+q$ that satisfies both these conditions.

Deriving the Expression for p+q

To find a relationship involving $p+q$, we can add the two given inequalities:

  1. Add Inequality (i) and Inequality (ii):

    $(3p - q) + (3q - p) < 4 + 12$

  2. Simplify the combined inequality:

    $3p - q + 3q - p < 16$

    Combine like terms:

    $2p + 2q < 16$

  3. Factor out 2 from the left side:

    $2(p + q) < 16$

  4. Divide both sides by 2 to isolate $p+q$:

    $\frac{2(p + q)}{2} < \frac{16}{2}$

    $p + q < 8$

This result, $p + q < 8$, represents the condition that must be satisfied by $p$ and $q$ to meet the initial inequalities.

Comparing with Options

Now, let's compare our derived condition $p + q < 8$ with the given options:

  • Option 1: $p+q<8$ - This exactly matches our derived condition.
  • Option 2: $p+q=8$ - This does not satisfy $p+q < 8$.
  • Option 3: $8 \le p+q < 16$ - This contradicts our finding that $p+q$ must be less than 8.
  • Option 4: $p+q \ge 16$ - This also contradicts our finding that $p+q$ must be less than 8.

Therefore, the expression $p+q < 8$ is the one that satisfies the given inequalities.

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Important Questions from Mathematical Inequalities

  1. A stick of length one meter is broken at two locations at distances of $b_1$ and $b_2$ from the origin (0), as shown in the figure. Note that $0 < b_1 < b_2< 1$. Which one of the following is NOT a necessary condition for forming a triangle using the three pieces?
    Note: All lengths are in meter. The figure shown is representative.

  2. Consider the following inequalities. 
    (i) $2x - 1 > 7$ 
    (ii) $2x - 9 < 1$ 
    Which one of the following expressions below satisfies the above two inequalities?

  3. Which one of the following is a representation (not to scale and in bold) of all values of $x$ satisfying the inequality  $2 – 5x \le \frac{6x-5}{3}$on the real numberline?

  4. The range of values of x satisfying the inequality $x^2 -3x+2 < 0$ is
  5. The number of solutions for the following system of inequalities is
    $X_1 \ge 0$
    $X_2 \ge 0$
    $X_1+ X_2 \le 10$
    $2X_1+ 2X_2 \ge 22$
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