How Long Did It Take?

Teaching elapsed time

Prerequisites: telling time to five minutes and to the minute, and knowing 60 minutes in an hour.

Suggested sequence (20 min)

1. Whole hours first: “3:00 to 6:00?” Count the hops of 1 hour.
2. Same minutes: “4:15 to 6:15?” Keep the minutes the same.
3. Number line: Draw hops from the start time: next hour, whole hours, last minutes. Use the tool above to check.
4. Check with clocks: Show both clocks and discuss how far the minute hand went round.

Common misconceptions

• Subtracting like decimals. 5:20 − 3:45 is not 2:35. There are 60 minutes in an hour.
• Counting the start time. From 9:00 to 12:00 is 3 hours, not 4.
• Mixing minutes and hours when adding the hops: 45 min + 1 hr + 40 min is not 86.

Questions to ask

• “What is the next whole hour after the start time? How far is that?”
• “How can you check your answer?” (Add the answer to the start time.)

Curriculum links

UK Year 3: compare durations of events. UK Year 4: solve problems involving converting from hours to minutes. US CCSS 3.MD.1: solve word problems involving addition and subtraction of time intervals in minutes. 4.MD.2: use the four operations to solve word problems involving intervals of time.

What your child is learning

Your child is learning to work out how long an activity lasted, from the start time to the finish time. They use hops on a number line instead of subtracting.

Why it can feel tricky

• Time uses 60 minutes in an hour, so normal subtraction doesn’t work.
• It uses several skills at once: reading the clock, counting on, and adding.

Easy ways to help at home

• Ask real questions: “It’s 4:20 and tea is at 5:00. How long to wait?”
• Time activities: “How long did the bath take?”
• Let your child draw a hop line on paper.
• Keep it short and playful. 2 or 3 minutes at a time is plenty.

Try this: “The film starts at 3:30 and lasts 1 hour 30 minutes. When does it end?” (5:00)