Difficulty: Medium
Correct Answer: p + 4
Explanation:
Introduction:
This algebraic word problem connects products and sums of two positive numbers expressed in terms of a parameter p. You are told that the product of two numbers is p, and then asked to compare the product after increasing both numbers by 2 with twice the sum of the original numbers. The question tests the ability to write symbolic expressions correctly and then simplify them carefully.
Given Data / Assumptions:
Concept / Approach:
First, expand the new product using distributive multiplication. Then subtract 2(a + b). Use the relation ab = p to express the answer in terms of p and constants only. This is a straightforward symbolic manipulation question, but it is easy to make sign or expansion mistakes if you rush.
Step-by-Step Solution:
Given: ab = p.New product = (a + 2)(b + 2).Expand: (a + 2)(b + 2) = ab + 2a + 2b + 4.Replace ab with p: new product = p + 2a + 2b + 4.Twice the sum of original numbers = 2(a + b) = 2a + 2b.Difference required = (new product) - (twice original sum).Difference = (p + 2a + 2b + 4) - (2a + 2b).Simplify: p + 2a + 2b + 4 - 2a - 2b = p + 4.So the new product is (p + 4) greater than twice the sum of the original numbers.
Verification / Alternative check:
Take a simple numeric example: let a = 2 and b = 3. Then p = ab = 6. New product = (2 + 2)(3 + 2) = 4 * 5 = 20. Twice the sum of originals = 2(2 + 3) = 2 * 5 = 10. Difference = 20 - 10 = 10. Our formula gives p + 4 = 6 + 4 = 10, which matches the calculation.
Why Other Options Are Wrong:
p or 2p: these ignore the constant increase that comes from adding 2 to both numbers.p + 2: underestimates the true difference, missing part of the constant term from the expansion.2p + 4: doubles p unnecessarily, not matching the derived expression.
Common Pitfalls:
Incorrectly expanding (a + 2)(b + 2), for example forgetting the +4 term.Not substituting ab = p correctly, or substituting at the wrong stage.Misinterpreting “how much greater” as a multiplicative comparison instead of a difference.
Final Answer:
p + 4
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