A rocket contained 467,000 kilograms (kg) of propellant before launch. Exactly 21 seconds after launch, 362,105 kg of this propellant...

1. TRANSLATE the problem information

• Given information:
  • Initial propellant: 467,000 kg
  • Remaining propellant after 21 seconds: 362,105 kg
  • Need to find: Average propellant burned per second
• This tells us we have a "before and after" situation where we need to find a rate

2. INFER the solution strategy

• To find average burned per second, we need two things:
  • Total amount burned (not given directly)
  • Total time (21 seconds - given)
• Strategy: First find total burned, then divide by time

3. Calculate total propellant burned

\(\mathrm{Total\ burned = Initial\ amount - Remaining\ amount}\)

\(\mathrm{Total\ burned = 467,000 - 362,105 = 104,895\ kg}\)

4. APPLY the average rate formula

\(\mathrm{Average\ burned\ per\ second = \frac{Total\ burned}{Time}}\)

\(\mathrm{Average\ burned\ per\ second = \frac{104,895}{21} = 4,995\ kg\ per\ second}\)

Answer: A. 4,995

Why Students Usually Falter on This Problem

Most Common Error Path:

Weak INFER skill: Students find the total propellant burned (104,895 kg) but stop there, thinking they've solved the problem.

They see 104,895 in the calculation and immediately look for it in the answer choices. Since Choice D is 104,895, they select it without realizing the question asks for the amount burned "each second," not the total amount burned.

This leads them to select Choice D (104,895).

The Bottom Line:

This problem tests whether students can distinguish between "total amount" and "rate per unit time." The key insight is recognizing that finding the total burned is just the first step - you must then divide by time to get the per-second rate.