A candle is made of 17 ounces of wax. When the candle is burning, the amount of wax in the...
GMAT Algebra : (Alg) Questions
A candle is made of \(\mathrm{17}\) ounces of wax. When the candle is burning, the amount of wax in the candle decreases by \(\mathrm{1}\) ounce every \(\mathrm{4}\) hours. If \(\mathrm{6}\) ounces of wax remain in this candle, for how many hours has it been burning?
3
6
24
44
1. TRANSLATE the problem information
- Given information:
- Candle starts with 17 ounces of wax
- Burns at rate of 1 ounce every 4 hours
- Currently has 6 ounces remaining
- Need to find: total hours of burning
2. INFER what we need to find first
- To use the burning rate, we first need to know how much wax has been consumed
- The consumed amount = original amount - remaining amount
3. Calculate wax consumed
- Wax consumed = \(17 - 6 = 11\) ounces
4. INFER how to apply the rate
- If 1 ounce burns in 4 hours, then 11 ounces will burn in 11 times as long
- This gives us: \(\mathrm{11}\) ounces \(\times\) \(\mathrm{4}\) hours/ounce
5. SIMPLIFY to find total time
- Total time = \(11 \times 4 = 44\) hours
Answer: D. 44
Why Students Usually Falter on This Problem
Most Common Error Path:
Weak TRANSLATE skill: Students might confuse what the "6 ounces" represents and try to work directly with the remaining wax instead of the consumed wax.
They might set up something like: \(\mathrm{6}\) ounces \(\times\) \(\mathrm{4}\) hours/ounce \(= 24\) hours, thinking this represents the burning time. This leads them to select Choice C (24).
Second Most Common Error:
Incomplete INFER reasoning: Students recognize they need to find consumed wax (11 ounces) but then incorrectly think: "If it takes 4 hours to burn 1 ounce, then it takes \(\frac{11}{4}\) hours to burn 11 ounces."
This backward reasoning leads to \(11 \div 4 = 2.75 \approx 3\) hours, causing them to select Choice A (3).
The Bottom Line:
This problem tests whether students can correctly identify what quantity to work with (consumed wax, not remaining wax) and properly apply rate relationships in the forward direction (more ounces = more time, not less time).
3
6
24
44