Split a sum with a linear condition: Divide 54 into two parts such that 10 times the first plus 22 times the second equals 780. What is the larger part?
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A24
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B34
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C30
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D32
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E20
Answer
Correct Answer: 34
Explanation
Introduction / Context:Partition problems with a linear condition are routine applications of two equations in two unknowns. Here, the total is fixed at 54 and a weighted sum equals 780. We will solve for the parts and identify the larger one.
Given Data / Assumptions:
- Let the first part be x and the second part be y.
- x + y = 54.
- 10x + 22y = 780.
Concept / Approach:Use substitution from x + y = 54 ⇒ y = 54 − x, then plug into the second equation and solve for x. This produces an exact integer solution, making identification of the larger part direct.
Step-by-Step Solution:
10x + 22(54 − x) = 78010x + 1188 − 22x = 780−12x = −408 ⇒ x = 34y = 54 − 34 = 20. Larger part = 34Verification / Alternative check:Compute 10*34 + 22*20 = 340 + 440 = 780, matching perfectly, while x + y = 54 holds.
Why Other Options Are Wrong:
- 24, 30, 32, 20: None satisfy both equations simultaneously as the larger part.
Common Pitfalls:Mixing up which variable you substituted, or solving 10x + 22y = 780 without using x + y = 54. Always leverage both equations.
Final Answer:34