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What is the solution of the inequality 21 − 7x ≤ 0?

Answer and explanation

Correct answer: x ≥ 3

The governing concept is solving an inequality with a negative coefficient and reversing the sign when dividing by that coefficient. Begin with 21 − 7x ≤ 0. Subtract 21 from both sides to obtain −7x ≤ −21. Divide by −7; because the divisor is negative, the less-than-or-equal sign reverses to greater-than-or-equal. Therefore x ≥ 3, so option A is correct. The endpoint is included because the original relation contains equality. Checking x = 3 gives 21 − 21 = 0, which satisfies the inequality. Values larger than 3 make 21 − 7x negative and also satisfy it. Option B results from failing to reverse the sign, while C and D incorrectly exclude or reverse the boundary.

Related tags

Linear InequalitiesNegative CoefficientSign ReversalInclusive BoundaryAlgebraic Solution Of Linear Inequalities In One VariableMathematicsClass 11 Mcq

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