JAMB 2020 Mathematics · Question 2

The sum of the interior angle of pentagon is 6x + 6y. Find y in terms of x.

Options

A.y = 6 - x
B.y = 90 - x
C.y = 120 - x
D.y = 150 - x

Answer: B. y = 90 - x

Explanation written with AI and checked against the answer key

Analyze the question: We're told the sum of the interior angles of a pentagon equals 6x + 6y, and we need y in terms of x. Concept: The sum of interior angles of an n-sided polygon is (n − 2) × 180°. For a pentagon, n = 5: Sum = (5 − 2) × 180° = 3 × 180° = 540° Solution: Set the expression equal to 540°: 6x + 6y = 540 Divide both sides by 6: x + y = 90 Make y the subject: y = 90 − x Tip: Memorize the formula (n − 2) × 180°. Common values to remember are triangle 180°, quadrilateral 360°, pentagon 540°, hexagon 720°. When an expression like 6x + 6y appears, look for a common factor to divide out quickly.

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