Questions: Calculating Elapsed Time Within an Hour

Question 1

A movie clip starts at 2:14 and ends at 2:47. A student counts up: 2:14 → 2:15 (1 min), then by fives to 2:45 (30 more min), then adds 2 ones to reach 2:47. What is the elapsed time?

• A. 61 minutes, by adding 14 + 47
• B. 33 minutes, by counting the total minutes added
• C. 27 minutes, by subtracting 47 - 14 incorrectly
• D. The elapsed time cannot be found without knowing the hour

Answer: (B)

Counting up: 1 + 30 + 2 = 33 minutes. The student hops from the start time forward in chunks — 1 minute to reach the nearest 5, then by fives, then individual ones — keeping a running total. This mirrors making change: count forward from the price until you reach the amount paid. Since both times are in the same hour (2:__), subtracting 47 - 14 = 33 also works as a shortcut.

Question 2

A class activity begins at 2:08 and ends at 2:44. Which approach correctly finds the elapsed time?

• A. 44 + 8 = 52 minutes
• B. Subtracting the minute values: 44 - 8 = 36 minutes
• C. Count backward from 2:44 to 2:08, which gives 36 minutes
• D. Elapsed time cannot be found because the hour digit is the same in both times

Answer: (B)

Since both times are within the same hour, you can directly subtract the minute values: 44 - 8 = 36 minutes. This arithmetic shortcut gives the same answer as counting up. Option A adds instead of subtracts. Counting backward (C) works but is harder than counting forward. Option D has it backwards — same-hour times are the easy case, not a barrier.

Question 3

Elapsed time is the amount of time between a start time and an end time — it answers the question 'how long did that take?'

• T. True
• F. False

Answer: True

Correct. Elapsed time is the duration between two clock readings. It is found by identifying the start and end times and calculating the gap — either by counting up from start to end, or by subtracting minute values when both times fall within the same hour.

Question 4

You can generally find elapsed time by subtracting the start minute value from the end minute value.

• T. True
• F. False

Answer: False

Subtracting minute values only works cleanly when both times are within the same hour. If a task starts at 1:48 and ends at 2:15, subtracting 48 from 15 gives a negative number, which is wrong. For cross-hour problems, counting up is the safer strategy: count from 1:48 to 2:00 (12 minutes), then 2:00 to 2:15 (15 minutes) = 27 minutes total.

Question 5

A game starts at 3:17 and ends at 3:52. Explain how to use the counting-up strategy to find the elapsed time.

Model answer: Start at 3:17 and hop forward in chunks: +3 minutes to reach 3:20, then count by fives — 3:25, 3:30, 3:35, 3:40, 3:45, 3:50 (30 more minutes), then +2 to reach 3:52. Total: 3 + 30 + 2 = 35 minutes.

Counting up is like making change — start at the beginning and add chunks until you reach the end, keeping a running total. The clock's 5-minute marks make counting by fives natural. Add all the chunks together to get the elapsed time. You can verify with subtraction: 52 - 17 = 35 minutes.