OC elapsed-time puzzles: 10 timeline questions

Quick Answer

To work out elapsed time, draw a timeline. Jump from the start time to the next whole hour, jump across the whole hours, then jump from the last whole hour to the finish time. Add the jumps, and take any break off at the end. This page from Braintree Coaching Australia has ten original questions for Year 3–4 children preparing for the NSW Opportunity Class (OC) test, two worked timeline models, a bus timetable to read and a reason for every wrong option. It is free, needs no sign-up, and takes about 30 minutes including review.

Who is this elapsed-time practice for?

This set suits a Year 3 or Year 4 child who can read an analogue or digital clock to the minute and knows there are 60 minutes in an hour. It is skill practice for mathematical reasoning. It is not a copy of official test items, and we do not claim a question like these will appear on the real test.

The NSW Department of Education describes the Opportunity Class Placement Test as a computer-based test with three sections: Reading, Mathematical Reasoning and Thinking Skills. All questions are multiple choice, and calculators are not permitted. The department's own OC practice tests are the place to see the real format.

All times on this page use am and pm. There is no 24-hour time.

How do you work out elapsed time on a timeline? Two worked models

Model 1: bridge the hour

A class starts at 2:35 pm and finishes at 4:10 pm. How long is it?

Draw a line and mark the start, each whole hour and the finish.

2:35 pm ──(+25 min)──> 3:00 pm ──(+60 min)──> 4:00 pm ──(+10 min)──> 4:10 pm

1. Jump from 2:35 to the next whole hour, 3:00. That is 25 minutes.
2. Jump across the whole hours, 3:00 to 4:00. That is 60 minutes.
3. Jump from 4:00 to the finish, 4:10. That is 10 minutes.
4. Add the jumps: 25 + 60 + 10 = 95 minutes, which is 1 hour 35 minutes.

Text version: three jumps of 25, 60 and 10 minutes, ending at 4:10 pm.

Model 2: cross midday

A walk starts at 11:25 am and finishes at 1:50 pm. How long is it?

11:25 am ──(+35 min)──> 12:00 pm ──(+60 min)──> 1:00 pm ──(+50 min)──> 1:50 pm

1. Jump from 11:25 am to 12:00 pm (midday). That is 35 minutes.
2. Jump from 12:00 pm to 1:00 pm. That is 60 minutes. This is the jump many children skip, because the clock goes from 12 to 1 and it feels like one number.
3. Jump from 1:00 pm to 1:50 pm. That is 50 minutes.
4. Add the jumps: 35 + 60 + 50 = 145 minutes, which is 2 hours 25 minutes.

Text version: three jumps of 35, 60 and 50 minutes, passing through 12:00 pm and 1:00 pm.

The questions

Work on paper. Draw the timeline each time, even if you think you can see the answer. Questions 9 and 10 use the bus timetable under Question 8.

Question 1. A reading group starts at 9:45 am and finishes at 11:20 am. How long is the group?

• A. 1 hour 75 minutes
• B. 1 hour 35 minutes
• C. 1 hour 15 minutes
• D. 2 hours 25 minutes

Question 2. A swimming lesson starts at 3:20 pm and finishes at 5:10 pm. How long is the lesson?

• A. 1 hour 40 minutes
• B. 2 hours 10 minutes
• C. 1 hour 50 minutes
• D. 1 hour 90 minutes

Question 3. An art class starts at 8:50 am and finishes at 10:15 am. How long is the class?

• A. 1 hour 25 minutes
• B. 1 hour 15 minutes
• C. 1 hour 65 minutes
• D. 2 hours 35 minutes

Question 4. A reading task starts at 11:40 am and finishes at 1:15 pm. How long does it take?

• A. 35 minutes
• B. 10 hours 25 minutes
• C. 2 hours 15 minutes
• D. 1 hour 35 minutes

Question 5. A bike ride starts at 10:35 am and finishes at 1:05 pm. How long is the ride?

• A. 2 hours 30 minutes
• B. 1 hour 30 minutes
• C. 2 hours 70 minutes
• D. 3 hours 5 minutes

Question 6. A workshop runs from 9:30 am to 12:10 pm. There is a 20-minute break in the middle. How long is the workshop without the break?

• A. 2 hours 40 minutes
• B. 3 hours
• C. 2 hours 20 minutes
• D. 2 hours

Question 7. A film starts at 1:15 pm and finishes at 3:40 pm. There is a 15-minute interval in the middle. How long is the film without the interval?

• A. 2 hours 25 minutes
• B. 2 hours 40 minutes
• C. 1 hour 55 minutes
• D. 2 hours 10 minutes

Question 8. Mia must arrive at the library at 3:05 pm. The trip takes 1 hour 25 minutes. What time must she leave?

• A. 2:20 pm
• B. 1:40 pm
• C. 4:30 pm
• D. 2:05 pm

Bus timetable for Questions 9 and 10. The Route 12 bus runs from Harbour Station to Beachside four times each morning. Each row is one bus run.

Route 12 morning bus timetable, Harbour Station to Beachside

Run	Harbour Station	Library	Market Square	Pool	Beachside
Run 1	8:05 am	8:17 am	8:36 am	8:51 am	9:14 am
Run 2	8:50 am	9:02 am	9:19 am	9:31 am	9:47 am
Run 3	9:35 am	9:47 am	10:08 am	10:22 am	10:41 am
Run 4	10:20 am	10:32 am	10:49 am	11:01 am	11:17 am

Question 9. Sam gets on at the Library on Run 3 and gets off at Beachside. How long is the ride?

• A. 45 minutes
• B. 94 minutes
• C. 54 minutes
• D. 57 minutes

Question 10. Priya leaves from Harbour Station and must be at Beachside by 10:00 am. Which is the latest run that gets her there on time, and when does it leave the station?

• A. Run 3, leaving at 9:35 am
• B. Run 1, leaving at 8:05 am
• C. Run 2, leaving at 9:47 am
• D. Run 2, leaving at 8:50 am

Answers and worked explanations

Check one question at a time. For each wrong answer, find the option your child chose and read why it is tempting.

Question 1 answer: B, 1 hour 35 minutes

9:45 to 10:00 is 15 minutes, 10:00 to 11:00 is 60 minutes and 11:00 to 11:20 is 20 minutes. 15 + 60 + 20 = 95 minutes. Option A (1 hour 75 minutes) subtracts the times as if they were ordinary numbers: 1120 − 945 = 175. Option C (1 hour 15 minutes) stops the timeline at 11:00 and leaves off the last 20 minutes. Option D (2 hours 25 minutes) takes the smaller minutes from the larger: 11 − 9 = 2 hours and 45 − 20 = 25 minutes.

Question 2 answer: C, 1 hour 50 minutes

3:20 to 4:00 is 40 minutes, 4:00 to 5:00 is 60 minutes and 5:00 to 5:10 is 10 minutes. 40 + 60 + 10 = 110 minutes. Option A (1 hour 40 minutes) stops at 5:00 and leaves off the last 10 minutes. Option B (2 hours 10 minutes) takes the smaller minutes from the larger: 5 − 3 = 2 hours and 20 − 10 = 10 minutes. Option D (1 hour 90 minutes) subtracts the times as numbers: 510 − 320 = 190.

Question 3 answer: A, 1 hour 25 minutes

8:50 to 9:00 is 10 minutes, 9:00 to 10:00 is 60 minutes and 10:00 to 10:15 is 15 minutes. 10 + 60 + 15 = 85 minutes. Option B (1 hour 15 minutes) forgets the 10-minute jump from 8:50 up to 9:00. Option C (1 hour 65 minutes) subtracts the times as numbers: 1015 − 850 = 165. Option D (2 hours 35 minutes) takes the smaller minutes from the larger: 10 − 8 = 2 hours and 50 − 15 = 35 minutes.

Question 4 answer: D, 1 hour 35 minutes

11:40 am to 12:00 pm is 20 minutes, 12:00 pm to 1:00 pm is 60 minutes and 1:00 pm to 1:15 pm is 15 minutes. 20 + 60 + 15 = 95 minutes. Option A (35 minutes) loses the hour between 12 and 1: 20 + 15 = 35. Option B (10 hours 25 minutes) ignores midday and subtracts the clock numbers, 11:40 − 1:15, as if both times were on the same side of 12. Option C (2 hours 15 minutes) rounds the start down to 11:00, which adds 40 minutes that were never part of the task.

Question 5 answer: A, 2 hours 30 minutes

10:35 to 11:00 is 25 minutes, 11:00 to 12:00 is 60 minutes, 12:00 to 1:00 is 60 minutes and 1:00 to 1:05 is 5 minutes. 25 + 60 + 60 + 5 = 150 minutes. Option B (1 hour 30 minutes) loses one of the hours when the clock goes from 12 back to 1. Option C (2 hours 70 minutes) adds 12 hours to the finish and subtracts as numbers: 1305 − 1035 = 270. Option D (3 hours 5 minutes) counts the 25 minutes from 10:35 to 11:00 as a whole hour.

Question 6 answer: C, 2 hours 20 minutes

9:30 to 10:00 is 30 minutes, 10:00 to 12:00 is 120 minutes and 12:00 to 12:10 is 10 minutes. 30 + 120 + 10 = 160 minutes, which is 2 hours 40 minutes from start to finish. Take the 20-minute break off: 160 − 20 = 140 minutes, which is 2 hours 20 minutes. Option A (2 hours 40 minutes) forgets the break. Option B (3 hours) adds the break instead of taking it off: 160 + 20 = 180. Option D (2 hours) takes the break off twice: 160 − 40 = 120.

Question 7 answer: D, 2 hours 10 minutes

1:15 to 2:00 is 45 minutes, 2:00 to 3:00 is 60 minutes and 3:00 to 3:40 is 40 minutes. 45 + 60 + 40 = 145 minutes, which is 2 hours 25 minutes from start to finish. Take the 15-minute interval off: 145 − 15 = 130 minutes, which is 2 hours 10 minutes. Option A (2 hours 25 minutes) forgets the interval. Option B (2 hours 40 minutes) adds the interval instead of taking it off. Option C (1 hour 55 minutes) takes the interval off twice: 145 − 30 = 115.

Question 8 answer: B, 1:40 pm

Work backwards from 3:05 pm. Go back the whole hour first: 3:05 pm to 2:05 pm. Then go back 25 minutes: 2:05 pm to 2:00 pm is 5 minutes, and 20 more minutes back from 2:00 pm is 1:40 pm. Option A (2:20 pm) takes the smaller minutes from the larger: 3 − 1 = 2 hours and 25 − 5 = 20 minutes. Option C (4:30 pm) adds the trip to the arrival time instead of taking it off. Option D (2:05 pm) takes off the hour and forgets the 25 minutes.

Question 9 answer: C, 54 minutes

Find the Run 3 row, then read from the Library column (9:47 am) to the Beachside column (10:41 am). 9:47 to 10:00 is 13 minutes and 10:00 to 10:41 is 41 minutes. 13 + 41 = 54 minutes. Option A (45 minutes) reads the Run 2 row, where Library to Beachside is 9:02 to 9:47. Option B (94 minutes) subtracts the times as numbers: 1041 − 947 = 94. Option D (57 minutes) reads the Run 1 row, where Library to Beachside is 8:17 to 9:14.

Question 10 answer: D, Run 2, leaving at 8:50 am

Look at the Beachside column for arrivals by 10:00 am. Run 1 arrives at 9:14 am and Run 2 arrives at 9:47 am. Run 3 arrives at 10:41 am, which is too late. The latest run on time is Run 2, which leaves Harbour Station at 8:50 am. Option A (Run 3, 9:35 am) picks the run by its leaving time, which is before 10:00, and does not check when it arrives. Option B (Run 1, 8:05 am) is on time but is not the latest. Option C (Run 2, 9:47 am) reads the arrival time at Beachside as the leaving time from the station.

What mistake patterns should we look for?

Tally which kind of error came up. Each one needs a different fix.

Pattern	Seen in	What to practise next
Subtracted the times as ordinary numbers ("1 hour 75")	Questions 1, 2, 3, 5, 9	Never write a minutes number above 59. Draw the jumps through the whole hours instead
Took the smaller number from the larger, hours and minutes separately	Questions 1, 2, 3, 8	Count up from the earlier time in jumps. Never subtract hours and minutes separately
Forgot the break, or added it instead of taking it off	Questions 6, 7	Work out start to finish first, then write "take off the break" as the last line
Lost an hour across 12 o'clock	Questions 4, 5	Always draw the 12:00 pm mark and the jump 12:00 to 1:00
Read the wrong timetable row	Questions 9, 10	Put a finger on the run's row and a second finger on the stop's column before reading the cell

Can my child try it with a real timetable?

Use the Route 12 timetable above, or pick a real bus or train timetable from your area.

Task. Priya wants to swim at the pool. The session starts at 10:30 am, and it is a 10-minute walk from the Pool bus stop to the entrance. She gets on at the Library. Which is the latest run that gets her there before the session starts, and how many minutes before the session does she reach the entrance?

Self-check.

1. Work backwards: she must reach the Pool stop by 10:20 am, because 10:20 plus a 10-minute walk is 10:30.
2. Look down the Pool column. Run 3 arrives at 10:22 am, which is 2 minutes too late. Run 2 arrives at 9:31 am.
3. The latest run on time is Run 2. She gets on at the Library at 9:02 am and arrives at the Pool stop at 9:31 am.
4. She reaches the entrance at 9:41 am, which is 49 minutes before the session starts.

If your child chose Run 3, go back to Model 1, work backwards from 10:20 am and read the Pool column again.

What should we do after this set?

• If two or more answers showed the same pattern in the table, repeat only those questions tomorrow with new times. Do not sit a full test yet.
• For mixed OC practice with worked solutions, open the OC practice tests guide.
• For full papers to sit under time, see the OC past papers page.
• The free mock tests need a free classroom account. Create one only when your child is ready for a timed sitting.
• For another OC skill, try the fractions on a number line set or the OC sample questions.
• If you want a structured set of full OC tests after that, see what the OC course includes and check it matches your child's entry year before buying.

Sources and review

Official source (checked 2026-10-15): NSW Department of Education, Opportunity Class practice tests: the test is computer-based with three sections (Reading, Mathematical Reasoning, Thinking Skills), and calculators are not permitted. The page lists no elapsed-time questions, so this page does not say the skill is tested.

Where the questions came from: all ten questions, both models and the bus timetable are original Braintree Coaching Australia material written for this page. The Route 12 bus and its stops are made up. None of it is taken from an official or third-party paper.

Author: James Rush, content writer, Braintree Coaching Australia.

Answer check: on 2026-10-15 every answer was recomputed and every wrong option checked by a second pass that had the key in front of it, so it tests the arithmetic and the wording, not a cold solve. A blind solve by someone who has not seen the keys and a named teacher review have not yet been recorded for this set. If you find an error, please tell us.

Last updated: 2026-10-15.