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An outdoor stage must be 130 centimeters tall. The base platform contributes 10 centimeters of height. The remaining height is...

GMAT Algebra : (Alg) Questions

Source: Prism
Algebra
Linear equations in 2 variables
EASY
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An outdoor stage must be \(130\) centimeters tall. The base platform contributes \(10\) centimeters of height. The remaining height is built using short riser blocks that are each \(6\) centimeters tall and tall riser blocks that are each \(8\) centimeters tall. If \(\mathrm{x}\) represents the number of short riser blocks and \(\mathrm{y}\) represents the number of tall riser blocks, which equation models this situation?

A

\(\mathrm{6x + 8y = 130}\)

B

\(\mathrm{6x + 8y + 10 = 130}\)

C

\(\mathrm{6x + 8y = 140}\)

D

\(\mathrm{x + y + 10 = 130}\)

Solution

1. TRANSLATE the problem information

  • Given information:
    • Total stage height needed: \(\mathrm{130\text{ cm}}\)
    • Base platform height: \(\mathrm{10\text{ cm}}\)
    • Short riser blocks: \(\mathrm{6\text{ cm}}\) each, x blocks used
    • Tall riser blocks: \(\mathrm{8\text{ cm}}\) each, y blocks used

2. INFER the relationship

  • The total height must equal the sum of all height contributions
  • Total height = Base platform + All short blocks + All tall blocks
  • We need: \(\mathrm{130 = 10 + 6x + 8y}\)

3. TRANSLATE this into standard equation form

  • Starting with: \(\mathrm{130 = 10 + 6x + 8y}\)
  • Rearranging: \(\mathrm{6x + 8y + 10 = 130}\)

This matches choice (B) \(\mathrm{6x + 8y + 10 = 130}\)

Answer: B




Why Students Usually Falter on This Problem


Most Common Error Path:

Weak TRANSLATE skill: Students forget to include the base platform in their equation setup.

They focus only on the variable blocks and write: \(\mathrm{6x + 8y = 130}\)

This leads them to select Choice A (\(\mathrm{6x + 8y = 130}\)) because they're only accounting for the riser blocks, not the complete height structure.


Second Most Common Error:

Poor TRANSLATE reasoning: Students misinterpret what equals \(\mathrm{130\text{ cm}}\).

They think the blocks alone need to provide \(\mathrm{140\text{ cm}}\) (130 + 10), writing: \(\mathrm{6x + 8y = 140}\)

This may lead them to select Choice C (\(\mathrm{6x + 8y = 140}\)) because they incorrectly added the base platform height to the target instead of recognizing it's part of the total.


The Bottom Line:

This problem tests whether students can correctly identify all components that contribute to a total and TRANSLATE that understanding into proper equation form. The key insight is recognizing that "\(\mathrm{130\text{ cm}}\) tall" means the entire structure, not just the blocks.

Answer Choices Explained
A

\(\mathrm{6x + 8y = 130}\)

B

\(\mathrm{6x + 8y + 10 = 130}\)

C

\(\mathrm{6x + 8y = 140}\)

D

\(\mathrm{x + y + 10 = 130}\)

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