Chapter 7 of 8

All 8 chapters
  1. 1Centimetres and metres, readunderstood
  2. 2Millimetres and kilometres, readunderstood
  3. 3Tenths and the decimal point, readunderstood
  4. 4Grams and kilograms, readunderstood
  5. 5Millilitres and litres, readunderstood
  6. 6Telling the time, readunderstood
  7. 7How long it takes, readunderstood
  8. 8Perimeter and area, readunderstood

M2.6.7 Chapter 7

How long it takes

A bus leaves at 09:40 and arrives at 11:15. How long is the journey?

Your guess

Pick one before you read on. It is fine to be wrong.

Your guess

  • You picked A. Read on. At the end, the chapter comes back to your guess.

  • You picked B. Read on. At the end, the chapter comes back to your guess.

  • You picked C. Read on. At the end, the chapter comes back to your guess.

By the end you can

  • Use clock faces to find how long from 09:40 to 11:15
  • Change hours to minutes and minutes to seconds
  • Count days and weeks on a calendar

A bus leaves at 09:40. It arrives at 11:15. How long is the journey?

Jump to the next hour first. Then jump a whole hour. Then jump to the end time.

Draw it first

Jump from the start to the end

  1. Two clock faces side by side. The left one shows "9:40" and the right one shows "11:15". Under them, step 2 adds "9:40 to 10:00 = 20 minutes" and "10:00 to 11:00 = 60 minutes". Step 3 adds "11:00 to 11:15 = 15 minutes". Step 4 adds "20 + 60 + 15 = 95 minutes" and "That is 1 hour 35 minutes".1234567891011129:4012345678910111211:15

    1 The bus leaves at 9:40. It arrives at 11:15.

  2. Two clock faces side by side. The left one shows "9:40" and the right one shows "11:15". Under them, step 2 adds "9:40 to 10:00 = 20 minutes" and "10:00 to 11:00 = 60 minutes". Step 3 adds "11:00 to 11:15 = 15 minutes". Step 4 adds "20 + 60 + 15 = 95 minutes" and "That is 1 hour 35 minutes".1234567891011129:4012345678910111211:159:40 to 10:00 = 20 minutes10:00 to 11:00 = 60 minutes

    2 Jump from 9:40 to 10:00. That is 20 minutes. Then jump to 11:00. That is 60 minutes.

  3. Two clock faces side by side. The left one shows "9:40" and the right one shows "11:15". Under them, step 2 adds "9:40 to 10:00 = 20 minutes" and "10:00 to 11:00 = 60 minutes". Step 3 adds "11:00 to 11:15 = 15 minutes". Step 4 adds "20 + 60 + 15 = 95 minutes" and "That is 1 hour 35 minutes".1234567891011129:4012345678910111211:159:40 to 10:00 = 20 minutes10:00 to 11:00 = 60 minutes11:00 to 11:15 = 15 minutes

    3 Jump from 11:00 to 11:15. That is 15 minutes.

  4. Two clock faces side by side. The left one shows "9:40" and the right one shows "11:15". Under them, step 2 adds "9:40 to 10:00 = 20 minutes" and "10:00 to 11:00 = 60 minutes". Step 3 adds "11:00 to 11:15 = 15 minutes". Step 4 adds "20 + 60 + 15 = 95 minutes" and "That is 1 hour 35 minutes".1234567891011129:4012345678910111211:159:40 to 10:00 = 20 minutes10:00 to 11:00 = 60 minutes11:00 to 11:15 = 15 minutes20 + 60 + 15 = 95 minutesThat is 1 hour 35 minutes

    4 Add the jumps. 20 + 60 + 15 = 95 minutes. That is 1 hour 35 minutes.

An hour is 60 minutes. A minute is 60 seconds. A second is one tick of a clock.

A table with two columns: "Time" and "is". The rows are: 1 hour, 60 minutes. 2 hours, 120 minutes. 1 minute, 60 seconds. 2 minutes, 120 seconds. 1 week, 7 days.Timeis1 hour60 minutes2 hours120 minutes1 minute60 seconds2 minutes120 seconds1 week7 days
Each hour has 60 minutes. Each minute has 60 seconds.

See it three ways

With things

Watch a clock. Wait until the long hand has gone once round. One hour has passed.

As a picture

Two clock faces. The left one shows "9:40" and the right one shows "10:40". Under them are the words "one hour later". The long hand is in the same place on both. The short hand has moved on one number.1234567891011129:4012345678910111210:40one hour later

In symbols

1 hour = 60 minutes. 2 hours = 2 × 60 = 120 minutes.

Three boxes in a row, each labelled 60 min. Under them is the label 3 hours.60 min60 min60 min3 hours
Each hour is a box of 60 minutes.

Worked example

How many minutes are in 3 hours?

  1. 1 hour is 60 minutes.
  2. 3 hours is 3 × 60 minutes.
  3. 3 × 60 = 180.

Answer: 180 minutes

Five boxes in a row, each labelled 60 s. Under them is the label 5 minutes.60 s60 s60 s60 s60 s5 minutes
Each minute is a box of 60 seconds, 60 s.

Worked example

How many seconds are in 5 minutes?

  1. 1 minute is 60 seconds.
  2. 5 minutes is 5 × 60 seconds.
  3. 5 × 60 = 300.

Answer: 300 seconds

A calendar shows days in rows of 7. Each row is one week. A week is 7 days.

Months have 28 to 31 days. This calendar shows 28 days.

A calendar of 14 days in 2 rows of 7, numbered 1 to 14. Day 3 and day 10 are shaded. Day 10 is one row below day 3.1234567891011121314
Go down one row and you move 7 days. Day 3 to day 10 is one week.

Worked example

Ana plants a seed on day 5. It sprouts 2 weeks later. Which day is that?

  1. 1 week is 7 days.
  2. 2 weeks is 2 × 7 = 14 days.
  3. Count on 14 days from day 5. 5 + 14 = 19.

Answer: day 19

Try it

Make a four week calendar

You need: a sheet of paper, a pencil, a ruler or a straight stick.

  1. Draw 4 rows of 7 squares. Use the ruler for straight lines.
  2. Write 1 to 7 in the top row. Write 8 to 14 in the next row.
  3. Keep going to 28.
  4. Shade day 2. Count on 7 days and shade that day. Keep going.

What you will see: The shaded days make a straight line down. Each one is 7 days after the one above.

If you cannot try it, this is what happens.
A calendar of 28 days in 4 rows of 7, numbered 1 to 28. Days 2, 9, 16 and 23 are shaded. They sit one above the other.12345678910111213141516171819202122232425262728

A wrong idea many people have

11:15 take away 9:40 is 1 hour 75 minutes.

Why it feels right: 1115 − 940 = 175. So it looks like 1 hour 75 minutes.

The test that breaks it: Count on from 9:40. One hour later is 10:40. Add 75 more minutes. That is 11:55, not 11:15.

What is true: An hour has 60 minutes, not 100. Jump to the next hour, then count on.

Key words

hour
60 minutes.
minute
60 seconds.
second
one tick of a clock. 60 seconds make a minute.
week
7 days.

Back to your guess

The answer is B: 1 hour 35 minutes.

It is 1 hour 35 minutes, which is 95 minutes. An hour has 60 minutes, not 100. So you cannot take times away like ordinary numbers.

Check yourself

Try each one before you look. A wrong answer tells you where to go next.

  1. How long is it from 08:50 to 10:20? Write hours and minutes.

    See the answer

    1 hour 30 minutes

    08:50 to 09:00 is 10 minutes. 09:00 to 10:00 is 60 minutes. 10:00 to 10:20 is 20 minutes. 10 + 60 + 20 = 90 minutes, which is 1 hour 30 minutes.

  2. A film starts at 14:30 and ends at 16:10. How long is the film?

    Tap your answer.

    1. Not this one. You took the times away like ordinary numbers: 1610 − 1430 = 180. An hour has 60 minutes, not 100. Try another.

    2. Yes, that is right. 14:30 to 15:00 is 30 minutes. 15:00 to 16:00 is 60 minutes. 16:00 to 16:10 is 10 minutes. 30 + 60 + 10 = 100 minutes, which is 1 hour 40 minutes.

    3. Not this one. You took 14 from 16, and 10 from 30. Jump instead. 14:30 to 15:00 is 30 minutes. Try another.

    See the answer

    1 hour 40 minutes

    14:30 to 15:00 is 30 minutes. 15:00 to 16:00 is 60 minutes. 16:00 to 16:10 is 10 minutes. 30 + 60 + 10 = 100 minutes, which is 1 hour 40 minutes.

    • If you chose A: You took the times away like ordinary numbers: 1610 − 1430 = 180. An hour has 60 minutes, not 100.
    • If you chose C: You took 14 from 16, and 10 from 30. Jump instead. 14:30 to 15:00 is 30 minutes.

  3. How many minutes are in 4 hours?

    See the answer

    240 minutes

    1 hour is 60 minutes. 4 × 60 = 240.

  4. How many seconds are in 3 minutes?

    See the answer

    180 seconds

    1 minute is 60 seconds. 3 × 60 = 180.

  5. Today is day 12. Kofi's seeds sprout 2 weeks later. Which day is that?

    See the answer

    day 26

    2 weeks is 2 × 7 = 14 days. 12 + 14 = 26.

  6. From an earlier chapter

    A jug holds 1 litre. Mei pours out 400 ml. How much water is left?

    Tap your answer.

    1. Not this one. You added. Pouring out takes water away. 1 litre is 1 000 ml, so take 400 from 1 000. Go to M2.6.5. Try another.

    2. Not this one. You used 500 ml for a litre. 1 litre is 1 000 ml. Take 400 from 1 000. Go to M2.6.5. Try another.

    3. Yes, that is right. 1 litre is 1 000 ml. 1 000 − 400 = 600.

    See the answer

    600 ml

    1 litre is 1 000 ml. 1 000 − 400 = 600.

    • If you chose A: You added. Pouring out takes water away. 1 litre is 1 000 ml, so take 400 from 1 000. Go to M2.6.5.
    • If you chose B: You used 500 ml for a litre. 1 litre is 1 000 ml. Take 400 from 1 000. Go to M2.6.5.

  7. A walk starts at 10:00 and ends at 13:00. How many hours is the walk?

    A time line with four marks. The labels are 10:00, 11:00, 12:00 and 13:00.10:0011:0012:0013:00
    Tap your answer.

    1. Not this one. You counted the 4 marks, and the first mark is the start. Count the gaps between the marks. Try another.

    2. Not this one. You counted only the marks in the middle, 11:00 and 12:00. Count the gaps between all the marks. Try another.

    3. Yes, that is right. The walk starts at 10:00. It goes to 11:00, then 12:00, then 13:00. That is 3 gaps, so 3 hours.

    See the answer

    3 hours

    The walk starts at 10:00. It goes to 11:00, then 12:00, then 13:00. That is 3 gaps, so 3 hours.

    • If you chose A: You counted the 4 marks, and the first mark is the start. Count the gaps between the marks.
    • If you chose B: You counted only the marks in the middle, 11:00 and 12:00. Count the gaps between all the marks.

  8. How many minutes is 1 hour 20 minutes?

    Tap your answer.

    1. Not this one. You counted 1 hour as 100 minutes. An hour is 60 minutes. So 60 + 20 = 80. Try another.

    2. Not this one. You added 1 and 20. The 1 is a whole hour, and an hour is 60 minutes. Try another.

    3. Yes, that is right. 1 hour is 60 minutes. 60 + 20 = 80 minutes.

    See the answer

    80 minutes

    1 hour is 60 minutes. 60 + 20 = 80 minutes.

    • If you chose A: You counted 1 hour as 100 minutes. An hour is 60 minutes. So 60 + 20 = 80.
    • If you chose B: You added 1 and 20. The 1 is a whole hour, and an hour is 60 minutes.

  9. Mei plants a seed on the shaded day. It sprouts one week later. Which day is that?

    A calendar of 14 days in 2 rows of 7, numbered 1 to 14. Day 4 is shaded.1234567891011121314
    Tap your answer.

    1. Not this one. You counted day 4 as the first of the 7 days. The 7 days begin after day 4. Try another.

    2. Yes, that is right. 1 week is 7 days. Count on 7 days from day 4. 4 + 7 = 11. That is one row down.

    3. Not this one. A week is 7 days. The seed sprouts 7 days after day 4, not on day 7. Try another.

    See the answer

    day 11

    1 week is 7 days. Count on 7 days from day 4. 4 + 7 = 11. That is one row down.

    • If you chose A: You counted day 4 as the first of the 7 days. The 7 days begin after day 4.
    • If you chose C: A week is 7 days. The seed sprouts 7 days after day 4, not on day 7.

  10. A game starts at 15:45 and ends at 16:30. How long is the game?

    A time line with three marks. The labels are 15:45, 16:00 and 16:30.15:4516:0016:30
    Tap your answer.

    1. Not this one. You took 30 from 45, the small minute from the big one. Jump instead. 15:45 to 16:00 is 15 minutes. 16:00 to 16:30 is 30 more. Try another.

    2. Not this one. You took the times away like ordinary numbers: 1630 − 1545 = 85. An hour has 60 minutes. Try another.

    3. Yes, that is right. 15:45 to 16:00 is 15 minutes. 16:00 to 16:30 is 30 minutes. 15 + 30 = 45 minutes.

    See the answer

    45 minutes

    15:45 to 16:00 is 15 minutes. 16:00 to 16:30 is 30 minutes. 15 + 30 = 45 minutes.

    • If you chose A: You took 30 from 45, the small minute from the big one. Jump instead. 15:45 to 16:00 is 15 minutes. 16:00 to 16:30 is 30 more.
    • If you chose B: You took the times away like ordinary numbers: 1630 − 1545 = 85. An hour has 60 minutes.

  11. How many seconds are in 4 minutes?

    Tap your answer.

    1. Not this one. You used 100 seconds for a minute. A minute is 60 seconds. 4 × 60 = 240. Try another.

    2. Yes, that is right. 1 minute is 60 seconds. 4 minutes are 4 × 60 = 240 seconds.

    3. Not this one. You added 4 to 60. Each minute is 60 seconds. So 4 minutes are 4 lots of 60. Try another.

    See the answer

    240 seconds

    1 minute is 60 seconds. 4 minutes are 4 × 60 = 240 seconds.

    • If you chose A: You used 100 seconds for a minute. A minute is 60 seconds. 4 × 60 = 240.
    • If you chose C: You added 4 to 60. Each minute is 60 seconds. So 4 minutes are 4 lots of 60.

Keep it

Copy this into your exercise book.

To find how long, jump to the next hour, then count on. 1 hour is 60 minutes. 1 minute is 60 seconds. 1 week is 7 days.

Draw: Two clocks, 9:40 and 11:15. Write the jumps 20, 60 and 15 under them.

Reading with a child? A short page for the adult: what this chapter teaches and three questions to ask.

No internet tomorrow? Save the whole book as one file (882 KB). It opens on any phone.