JAMB 2015 Economics · Question 62

Given that the prices and quantities supplied in litres of petrol is expressed as Qs = 25 + 0.25P. Qs is the…

Question

Given that the prices and quantities supplied in litres of petrol is expressed as Qs = 25 + 0.25P. Qs is the quantity supplied and P is the price. Determine the quantity supplied when the price per liter is N30

A.50litres
B.32.5litres
C.30litres
D.35litres

Answer: B. 32.5litres

Explanation written with AI and checked against the answer key

Analyze the question: You are given a supply function, Qs = 25 + 0.25P. You need the quantity supplied (Qs) when the price P = ₦30. Concept: A supply function links price to quantity supplied. To find Qs at a given price, substitute the price into the equation and simplify. Solution: Qs = 25 + 0.25P Substitute P = 30: Qs = 25 + 0.25(30) Qs = 25 + 7.5 Qs = 32.5 litres Answer: B, 32.5 litres Tip: In "substitute and solve" questions, plug in the value carefully and do the multiplication before the addition. Here 0.25 × 30 is the same as ¼ of 30, which is 7.5. Turning decimals into fractions (0.25 = ¼) often makes mental arithmetic faster in the exam hall.

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