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A contest prize of $200 is divided between two winners. The first winner receives $x and the second winner receives...

GMAT Algebra : (Alg) Questions

Source: Prism
Algebra
Systems of 2 linear equations in 2 variables
MEDIUM
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Notes
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A contest prize of \(\$200\) is divided between two winners. The first winner receives \(\$x\) and the second winner receives \(\$y\). The first winner receives \(\$20\) more than \(3\) times what the second winner receives. What is the value of x?

A

45

B

140

C

150

D

155

Solution

1. TRANSLATE the problem information

  • Given information:
    • Total prize = \(\$200\) (split between two winners)
    • First winner receives \(\$x\), second winner receives \(\$y\)
    • First winner receives \(\$20\) more than 3 times what second winner receives
  • What this tells us mathematically:
    • \(\mathrm{x + y = 200}\)
    • \(\mathrm{x = 3y + 20}\)

2. INFER the solution approach

  • We have two equations with two unknowns - this is a system of equations
  • Since the second equation already isolates x, substitution method will work efficiently
  • Strategy: substitute the expression for x into the first equation

3. SIMPLIFY using substitution

  • Substitute \(\mathrm{x = 3y + 20}\) into \(\mathrm{x + y = 200}\):
    • \(\mathrm{(3y + 20) + y = 200}\)
    • \(\mathrm{4y + 20 = 200}\)
    • \(\mathrm{4y = 180}\)
    • \(\mathrm{y = 45}\)

4. SIMPLIFY to find x

  • Now that \(\mathrm{y = 45}\), substitute back:
    • \(\mathrm{x = 3(45) + 20}\)
    • \(\mathrm{x = 135 + 20}\)
    • \(\mathrm{x = 155}\)

Answer: D. 155




Why Students Usually Falter on This Problem


Most Common Error Path:

Weak TRANSLATE skill: Students struggle to convert "20 more than 3 times what the second winner receives" into the equation \(\mathrm{x = 3y + 20}\). They might write incorrect relationships like:

  • \(\mathrm{x = 3y - 20}\) (subtracting instead of adding)
  • \(\mathrm{x = 3(y + 20)}\) (misplacing the parentheses)
  • \(\mathrm{3x + 20 = y}\) (completely backwards relationship)

Any of these translation errors leads to a different system of equations and an incorrect final answer that doesn't match any given choice, causing confusion and guessing.


Second Most Common Error:

Poor SIMPLIFY execution: Students correctly set up the equations but make algebraic errors when solving \(\mathrm{4y + 20 = 200}\). Common mistakes include:

  • Forgetting to subtract 20 from both sides: \(\mathrm{4y = 200}\), so \(\mathrm{y = 50}\)
  • Arithmetic errors: \(\mathrm{200 - 20 = 160}\) (instead of 180), leading to \(\mathrm{y = 40}\)

These errors cascade to wrong values of x, potentially leading them to select Choice B (140) or other incorrect options.


The Bottom Line:

This problem tests whether students can accurately translate complex verbal relationships into mathematical equations. The phrase "20 more than 3 times" requires careful parsing - students must recognize the order of operations in language and convert it precisely to algebra.

Answer Choices Explained
A

45

B

140

C

150

D

155

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