A recorded segment on a timeline begins at 1:00 and ends at 5:00. At a certain moment, the timestamp shows...

1. TRANSLATE the timeline information

• Given information:
  • Segment begins at 1:00
  • Segment ends at 5:00
  • Current timestamp shows 2:00
  • Need to find what percent has elapsed

2. INFER the approach needed

• This is asking for elapsed time as a percentage of total time
• We need: \((\text{elapsed time} \div \text{total duration}) \times 100\%\)
• First find total duration, then elapsed time

3. Calculate the total duration

• Total duration = End time - Start time
• Total duration = \(5:00 - 1:00 = 4:00\) (4 minutes)

4. Calculate the elapsed time

• Elapsed time = Current time - Start time
• Elapsed time = \(2:00 - 1:00 = 1:00\) (1 minute)

5. SIMPLIFY to find the percentage

• Percent elapsed = \((\text{elapsed} \div \text{total}) \times 100\%\)
• Percent elapsed = \((1 \div 4) \times 100\%\)
• Percent elapsed = \(0.25 \times 100\% = 25\%\)

Answer: B (25%)

Why Students Usually Falter on This Problem

Most Common Error Path:

Weak TRANSLATE reasoning: Students might confuse what represents the "part" versus the "whole" in this timeline context.

Some students calculate \((2:00 \div 5:00) \times 100\% = 40\%\), thinking the current timestamp (2:00) should be compared directly to the end time (5:00), ignoring that the segment doesn't start at 0:00.

This may lead them to select Choice C (40%)

Second Most Common Error:

Inadequate SIMPLIFY execution: Students correctly set up \((1 \div 4) \times 100\%\) but make arithmetic errors in the final calculation.

They might incorrectly convert \(\frac{1}{4}\) to 20% instead of 25%, possibly confusing it with \(\frac{1}{5} = 20\%\).

This may lead them to select Choice A (20%)

The Bottom Line:

Timeline problems require careful attention to what represents the starting reference point - students must recognize that elapsed time is measured from the segment's start time, not from time zero.