An event offered two time slots, morning and afternoon. A city report states that 60% of attendees chose the afternoon...
GMAT Algebra : (Alg) Questions
An event offered two time slots, morning and afternoon. A city report states that \(\mathrm{60\%}\) of attendees chose the afternoon slot. A ticketing summary states that \(\mathrm{180}\) more attendees chose the afternoon slot than the morning slot. Based on these data, how many attendees chose the morning slot?
\(180\)
\(270\)
\(360\)
\(540\)
1. TRANSLATE the problem information
- Given information:
- \(60\%\) of attendees chose afternoon slot
- 180 more people chose afternoon than morning
- Need to find morning attendees
2. INFER the complementary relationship
- If \(60\%\) chose afternoon, then \(40\%\) chose morning (percentages must add to \(100\%\))
- Let \(\mathrm{T}\) = total attendees
- \(\mathrm{Afternoon} = 0.60\mathrm{T}\), \(\mathrm{Morning} = 0.40\mathrm{T}\)
3. TRANSLATE the difference statement into an equation
- "180 more chose afternoon than morning" means:
- \(\mathrm{Afternoon} - \mathrm{Morning} = 180\)
- \(0.60\mathrm{T} - 0.40\mathrm{T} = 180\)
4. SIMPLIFY to solve for total attendees
- \(0.60\mathrm{T} - 0.40\mathrm{T} = 0.20\mathrm{T} = 180\)
- \(\mathrm{T} = 180 \div 0.20 = 900\) total attendees
5. SIMPLIFY to find morning attendees
- \(\mathrm{Morning} = 0.40\mathrm{T} = 0.40 \times 900 = 360\)
Answer: (C) 360
Why Students Usually Falter on This Problem
Most Common Error Path:
Weak TRANSLATE skill: Students misinterpret "180 more chose afternoon" and think this means 180 people chose afternoon total, rather than understanding it's the difference between the two groups.
They might set up: \(\mathrm{Afternoon} = 180\), \(\mathrm{Morning} = ?\), leading to confusion about how to use the \(60\%\) information. This leads to confusion and guessing.
Second Most Common Error:
Incomplete SIMPLIFY execution: Students correctly find \(\mathrm{T} = 900\) but then calculate the afternoon attendees (\(0.60 \times 900 = 540\)) instead of the morning attendees that the question asks for.
This may lead them to select Choice (D) (540).
The Bottom Line:
This problem requires careful reading to distinguish between the total in each group versus the difference between groups, combined with understanding that percentage splits are complementary.
\(180\)
\(270\)
\(360\)
\(540\)