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NSW SelectiveYear 7 entry

Time calculations for the Selective maths test

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Time calculations are hard because time counts in sixties, not tens. For Selective maths, find a time gap with the bridge method: hop to the next whole hour, hop whole hours, hop the last minutes, then add the hops.

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The full lesson is in the SelectiveReady app. A free account opens How and Why Authors Write; this lesson needs a paid plan.

Updated 16 October 2026 · Facts checked 12 October 2026

Time Calculations (lesson preview)

A short preview from the SelectiveReady lesson “Time Calculations”, on time calculations for the NSW Selective test.

Published:

Read the video transcript

We start at 9:45. Our first hop is to the nearest friendly hour, which is 10 am. How long is that hop? Easy, 15 minutes. Okay, now we're at 10 am. Let's make a big hop to the next hour, 11 am. That's exactly one hour or 60 minutes. And for our last little hop, we just go from 11 am to our finish time, 11:20 am. That's just 20 minutes. See, three simple little jumps. And now for the best part, the easiest maths you'll do all day. We just add up the minutes from our three hops. So 15 plus 60 plus 20 gives us a grand total of 95 minutes. And just like that, we have the total journey time. The very last step is to make that look like a proper time. We know an hour is 60 minutes, right? So we pull one hour, that's 60 minutes, out of our 95. And what's left over? 35 minutes. And there it is. Our final answer, one hour and 35 minutes.

Time Calculations is a full lesson in the SelectiveReady app; the preview here has English and Chinese captions. A free account opens one lesson, How and Why Authors Write; the other lessons need a paid plan1SelectiveReady · 13 October 2026 · Published.

2

What will your child learn in this lesson?

Your child learns why time questions trip up even strong students, and a method that works every time. They'll be able to change between 12-hour and 24-hour time, find a time gap with the bridge method and read a timetable without rushing.

The clip finds how long a train trip from 9:45 am to 11:20 am takes, in three hops. The full lesson adds 24-hour time, the midnight and noon trap, timetables and a five-point cheat sheet.

3

Why are time calculations tricky?

Our number system counts in tens, but time counts in sixties: 60 seconds in a minute and 60 minutes in an hour. The lesson calls this the clash that makes brains short-circuit. A sum that works for ordinary numbers gives a time that can't exist.

How do 12-hour and 24-hour time work?

From 1 pm to 11:59 pm, add 12 to the hour, but 12:30 pm stays 12:30. A new day starts at zero, so midnight is 00:00 and noon is 12:00.

12-hour time24-hour timeHow
12:00 midnight00:00The day starts at zero
7:15 am07:15Morning times keep their hour
12:00 noon12:00Twelve hours have passed
1:00 pm13:00Add 12 to the hour
5:30 pm17:30Add 12 to the hour
11:59 pm23:59The last minute of the day
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How do time questions show up in the Selective test?

In our practice sets, they come as clock faces, timetables, trips and clocks that run fast. The Department publishes no topic list, so the number of time questions isn't known. 2NSW Education · 13 October 2026 · Published

The Department's ruleWhat it means for time
Questions use concepts your child already learns at school2NSW Education · 12 October 2026 · PublishedClocks and timetables are school maths
No calculator2NSW Education · 12 October 2026 · Published in any sectionA calculator wouldn't help anyway: it counts in tens
23NSW Education · 12 October 2026 · Published sheets of working paper, with more on requestRoom to draw a bridge for each question
352NSW Education · 12 October 2026 · Published questions in 402NSW Education · 12 October 2026 · Published minutesA little over a minute each, so a reliable method beats a clever one
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What is the bridge method for time gaps?

Instead of one messy subtraction, your child makes small hops to friendly times and adds them up. The lesson calls it almost impossible to get wrong.

The bridge method: from the start, hop to the next whole hour, hop whole hours, hop the last minutes to the finish, then add the hops.

  1. Hop to the next whole hour

    From the start time to the next o'clock. Write the minutes above the hop.

  2. Hop whole hours

    Jump in hours until you reach the hour of the finish time.

  3. Hop the last minutes

    From that o'clock to the finish time.

  4. Add the hops, then tidy up

    Add the minutes. Every 60 minutes becomes one hour.

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What does a worked time question look like?

We wrote this question to show the bridge across noon, with 24-hour times like a real timetable.

Question: A bus leaves Bathurst at 10:50 and arrives in Sydney at 13:25. How long is the trip?

HopFrom and toTime
To the next whole hour10:50 to 11:0010 minutes
Whole hours11:00 to 13:002 hours
The last minutes13:00 to 13:2525 minutes
Add the hops10 + 25 = 35 minutes, plus 2 hours2 hours 35 minutes

Check: 13:25 is 1:25 pm, and 10:50 am to 1:25 pm is a little over two and a half hours. The answer fits.

Subtracting like ordinary numbers gives 13.25 − 10.50 = 2.75. That looks like 2 hours 75 minutes, which isn't a real time.

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What is the most common time mistake?

The most common mistake is subtracting times as if they were ordinary numbers. The lesson's warning: if an answer has more than 59 minutes in it, you've gone down the wrong path.

TrapWhat it looks likeThe fix
Subtracting like decimals11.20 − 9.45 = 1.75Use the bridge: 1 hour 35 minutes
Midnight and noonMidnight written as 24:00 or 12:00Midnight is 00:00, noon is 12:00
Rushing a timetableTaking the time from the wrong rowTrace the row and column with a finger
Rounding the minutes55 minutes treated as an hourHop the exact minutes
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Can my child try one on their own?

Here is a question from our free maths set: a lesson that starts at the time on a clock face and lasts 55 minutes. Your child reads the clock, then builds a bridge.

Practice question · SEL-MA-TST-16

The clock shows the time Jarrah's swimming lesson starts on Saturday morning.

The lesson lasts 55 minutes. At what time does it finish?

  1. A

    8:45 am

  2. B

    10:03 am

  3. C

    10:35 am

  4. D

    10:40 am

  5. E

    11:35 am

Show answer and explanation

Answer: C

Answer: C (10:35 am)

  1. The long hand points at 8, which is 40 minutes past the hour. The short hand is between 9 and 10, so the lesson starts at 9:40 am.
  2. 20 minutes takes the time to 10:00 am. That leaves 55 − 20 = 35 minutes.
  3. The lesson finishes at 10:35 am.

Why the other options are wrong

  • A (8:45 am): This takes 55 minutes away from the start time instead of adding it.
  • B (10:03 am): This reads the long hand pointing at 8 as 8 minutes past, so it starts from 9:08 am.
  • D (10:40 am): This rounds 55 minutes up to a whole hour.
  • E (11:35 am): This reads the short hand, which is close to 10, as 10 o'clock, so it starts from 10:40 am.

  1. Read the clock

    The long hand points at 8, which is 40 minutes past. The short hand is between 9 and 10, so it's 9:40 am.

  2. Hop to the whole hour

    9:40 to 10:00 is 20 minutes. That leaves 55 − 20 = 35 minutes.

  3. Hop the rest

    10:00 plus 35 minutes is 10:35 am. The answer is C.

  4. Check the traps

    B reads the long hand at 8 as 8 minutes past. D rounds 55 minutes up to an hour.

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Questions parents ask about time calculations

What is 3 pm in 24-hour time?

15:00. Add 12 to the hour for any time from 1 pm to 11:59 pm.

Does my child need to read an analogue clock?

Yes, it helps. Our try-it question shows a clock face, and the hands hold the first step.

How do you work out elapsed time?

Elapsed time is the gap between two times. Use the bridge method: hop to whole hours, then add the hops.

How can my child practise at home?

Plan a day out with a real bus or train timetable together. Ask how long each part takes and when you need to leave.

Is the full lesson free?

A free account opens one lesson, How and Why Authors Write; the other lessons need a paid plan1SelectiveReady · 13 October 2026 · Published.

Next questions

Selective Mathematical Reasoning →Lesson: Measurement and Units →Lesson: Ratio & Rate →Lesson: Reading Charts and Graphs →Free Selective practice test →

Sources and checks

  1. SelectiveReady

    SelectiveReady · Checked 13 October 2026

  2. Selective high school practice tests

    NSW Department of Education · Checked 12 October 2026 · Practice materials: personal or non-commercial use only; CC BY 4.0 does not apply (page notice). Page text: CC BY 4.0.

  3. Placement test

    NSW Department of Education · Checked 12 October 2026 · CC BY 4.0 (NSW Department of Education copyright notice); quotes credited

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