If the Celsius temperature of Object X is C and the equivalent Fahrenheit temperature of Object X is F, then...
GMAT Data Sufficiency : (DS) Questions
If the Celsius temperature of Object X is C and the equivalent Fahrenheit temperature of Object X is F, then \(\mathrm{F} = \frac{9}{5}\mathrm{C} + 32\). Is the Celsius temperature of Object X greater than 50?
- \(\mathrm{F} > 120\)
- \(\mathrm{F} - \mathrm{C} > 72\)
Understanding the Question
We need to determine whether the Celsius temperature of Object X is greater than 50°C.
Given the relationship \(\mathrm{F} = \frac{9}{5}\mathrm{C} + 32\), let's find a key reference point: when \(\mathrm{C} = 50\), we get \(\mathrm{F} = \frac{9}{5}(50) + 32 = 90 + 32 = 122°\mathrm{F}\).
So our question essentially becomes: Is F > 122°F?
For this yes/no question to be sufficient, we need information that definitively tells us either:
- YES, C is always greater than 50, or
- NO, C is always 50 or less
Analyzing Statement 1
Statement 1 tells us: \(\mathrm{F} > 120\)
Let's test specific scenarios to see if this guarantees \(\mathrm{C} > 50\):
Test Case 1: What if \(\mathrm{F} = 121°\mathrm{F}\)?
- This satisfies \(\mathrm{F} > 120\) ✓
- But since 121 < 122, this would mean \(\mathrm{C} < 50\)
- Answer to our question: NO
Test Case 2: What if \(\mathrm{F} = 125°\mathrm{F}\)?
- This satisfies \(\mathrm{F} > 120\) ✓
- Since 125 > 122, this would mean \(\mathrm{C} > 50\)
- Answer to our question: YES
Since we can get different answers (both YES and NO are possible), Statement 1 is NOT sufficient.
[STOP - Not Sufficient!] This eliminates choices A and D.
Analyzing Statement 2
Now let's forget Statement 1 completely and analyze Statement 2 independently.
Statement 2 tells us: \(\mathrm{F} - \mathrm{C} > 72\)
Here's the key insight: Let's examine what happens to the difference \((\mathrm{F} - \mathrm{C})\) as C changes.
When \(\mathrm{C} = 50\), we know \(\mathrm{F} = 122\), which means \(\mathrm{F} - \mathrm{C} = 122 - 50 = 72\) exactly.
The crucial observation: As C increases, the gap \((\mathrm{F} - \mathrm{C})\) also increases. Why? Because when converting from Celsius to Fahrenheit, we multiply by 9/5 (which is 1.8, greater than 1) before adding 32. This multiplication creates an ever-widening gap.
Therefore:
- If \(\mathrm{F} - \mathrm{C} = 72\), then \(\mathrm{C} = 50\)
- If \(\mathrm{F} - \mathrm{C} > 72\), then \(\mathrm{C} > 50\)
Since Statement 2 tells us \(\mathrm{F} - \mathrm{C} > 72\), we can definitively conclude \(\mathrm{C} > 50\).
[STOP - Sufficient!] Statement 2 is sufficient.
This eliminates choices C and E.
The Answer: B
Since Statement 2 alone is sufficient but Statement 1 alone is not sufficient, the answer is B.
Answer Choice B: "Statement 2 alone is sufficient, but Statement 1 alone is not sufficient."