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3rd Grade · 3.MD.A.1

Elapsed time in 3rd grade

Elapsed time is the amount of time that passes from the start of something to its end. In 3rd grade, your child learns to read a clock to the nearest minute and to find how many minutes an activity lasts. Your child also solves elapsed time word problems by drawing jumps on a number line.

What the standard says

The official Common Core wording, quoted exactly. The plain version follows.

3.MD.A.1 Tell and write time to the nearest minute and measure time intervals in minutes. Solve word problems involving addition and subtraction of time intervals in minutes, e.g., by representing the problem on a number line diagram.

What it means, in plain words

Telling time to the nearest minute starts with the minute hand, the long hand on the clock. Each small mark between two numbers stands for 1 minute. Your child counts by fives up to the last number the minute hand has passed, then counts on by ones. The hour hand, the short hand, shows the last hour it has passed.

To find elapsed time, many classes use a number line marked with times. Your child starts at the start time, jumps to the next full hour, then jumps to the end time. Adding the jumps gives the elapsed time in minutes. The jump to the full hour matters, because an hour has 60 minutes, not 100.

Elapsed time word problems ask one of three things: how long something lasted, when it ended or when it started. To find an end time, your child adds minutes to the start time. To find a start time, your child counts back from the end time.

Your child should be able to:

  • Read a clock with hands to the nearest minute and write the time, such as 7:22
  • Find how many minutes pass between a start time and an end time
  • Find an end time or a start time when the number of minutes is given
  • Show the jumps of time on a number line

Example

A movie starts at 6:40 and ends at 7:15. How long is the movie?

  1. Mark 6:40, 7:00 and 7:15 on a number line.
  2. From 6:40 to 7:00 is a jump of 20 minutes.
  3. From 7:00 to 7:15 is a jump of 15 minutes.
  4. 20+15=3520 + 15 = 35, so the movie is 35 minutes long.

Example

Swim practice starts at 4:50 and lasts 45 minutes. What time does it end?

  1. Split the 45 minutes into 10 minutes and 35 minutes.
  2. A jump of 10 minutes from 4:50 reaches 5:00.
  3. A jump of 35 minutes from 5:00 reaches 5:35.
  4. Swim practice ends at 5:35.

Where children usually get stuck

  • For a movie from 6:40 to 7:15, your child subtracts 640 from 715 and says the movie lasts 75 minutes.

    The times are treated like ordinary numbers, where 100 ones make the next hundred. An hour has only 60 minutes, so subtracting the digits gives the wrong answer.

    What helps. Draw a line and mark the start and end times. Jump to the full hour first, then count the two jumps together.

  • At 7:50, your child reads the clock as 8:50.

    At 7:50 the hour hand sits very close to the 8. The hour hand shows the last hour it has passed, and it has not passed the 8 yet.

    What helps. On a real clock, turn the minute hand slowly once around and watch the hour hand creep from the 7 to the 8.

  • Your child adds 30 minutes to 3:45 and writes 3:75.

    The minutes were added correctly, but 75 minutes is more than 1 hour. After 59 minutes, the clock starts a new hour.

    What helps. Ask what comes after 3:59 on a digital clock. Then add in two steps: up to the full hour, then the rest. The answer is 4:15.

Try four practice questions

Real 3rd grade questions from our question bank, easiest first. Answer them right here, check each one, and see a worked solution for any question.

  1. 1Warm-up
    Art class starts at 2:10 and lasts 30 minutes. What time does art class end?
    A
    2:45
    B
    1:40
    C
    2:40
    D
    3:40
    Show the answer and how to solve it

    Art class ends at 2:40.

    1. 1Read the problem: art class starts at 2:10 and lasts 30 minutes. To find the end time, add 30 minutes to 2:10.
    2. 2Add the minutes: 10+30=4010 + 30 = 40. Since 40 is less than 60, the hour stays at 2 and the new minute count is 40. Art class ends at 2:40.

    Common mistake. A common mistake is subtracting 30 minutes from 2:10 and getting 1:40. The duration tells how long after the start time the activity ends — add 30 minutes to find when art class ends.

    The idea underneath. Adding time works like adding numbers with regrouping — when the minutes add up to more than 60, the extra carries forward into the next hour.

  2. 2On level
    Jordan's soccer practice lasted 60 minutes. The team spent 20 minutes doing drills, and the rest of the time was scrimmage games. Which expression shows how many minutes the team spent on scrimmage?
    A
    60−20\displaystyle 60 - 20
    B
    60+\displaystyle 60 + {}
    20\displaystyle 20
    C
    20−60\displaystyle 20 - 60
    D
    60−20−20\displaystyle 60 - 20 - 20
    Show the answer and how to solve it

    The expression 60−2060 - 20 correctly shows the scrimmage time. The whole practice was 6060 minutes, so subtracting the 2020 minutes of drills leaves the time spent on scrimmage.

    1. 1First, find what we know. The whole practice lasted 6060 minutes. The team spent 2020 minutes doing drills.
    2. 2We want the time spent on scrimmage. The practice is split into two parts: drills and scrimmage. We know the whole and one part, so we take the part away from the whole. That means subtracting.
    3. 3The expression is the whole minus the drill time:

    Common mistake. A common mistake is writing 60+2060 + 20 instead of subtracting. The 6060 minutes is the WHOLE practice; the 2020 minutes is one PART. To find the other part, subtract the known part from the whole: 60−2060 - 20.

    The idea underneath. When a whole is split into known parts, finding any unknown part means subtracting the known part(s) from the whole.

  3. 3On level
    Carlos wants to find what time will be 45 minutes after the time shown. Carlos says the end time is 3:10.
    123456789101112
    Carlos's work:
    25 + 45 = 70 minutes
    70 minutes = 1 hour 10 minutes
    Hour: 3 + 0 = 3
    End time: 3:10
    Select the statement that best describes Carlos's work.
    A
    Carlos's end time should be 4:10; Carlos missed the hour rollover, getting 3:10.
    B
    Carlos's end time should be 4:10; Carlos subtracted 45 minutes instead of adding them, getting 2:40 instead.
    C
    Carlos's end time of 3:10 is correct.
    D
    Carlos's end time should be 4:10; Carlos added the minutes incorrectly, getting 4:20.
    Show the answer and how to solve it

    The correct end time is 4:10, not 3:10. Carlos kept the hour at 3 instead of advancing to 4 when the minutes passed 60. The matching statement names the missing-hour-rollover error and gives the correct end time of 4:10.

    1. 1Look at the start time on the clock: it shows 3:25.
    2. 2Add 45 minutes to 3:25. From 3:25, 35 more minutes brings you to 4:00 (crossing into the 4 o'clock hour). Then 10 more minutes brings you to 4:10. The correct end time is 4:10.
    3. 3Carlos's work finds 1 hour 10 minutes but leaves the hour at 3. Add that 1 hour to 3. The end time is 4:10.

    Common mistake. A common mistake is keeping the hour the same when the minutes pass 60 — for example, saying 3:10 instead of 4:10 when adding 45 minutes to 3:25. Always advance the hour when the total minutes cross 60.

    The idea underneath. Adding minutes that cross an hour boundary requires advancing the hour by one. The minutes 'roll over' from one hour to the next, just like seconds roll over to minutes when they reach 60.

  4. 4Stretch
    Marco wants to find the start time. His reading lasted 25 minutes and finished at 3:45. Marco says the start time is 3:20. Select the statement that best describes Marco's answer.
    A
    Marco subtracted from the hour instead of the minutes, getting 2:45 instead of 3:20.
    B
    Marco's calculation is correct.
    C
    Marco added instead of subtracting, getting 4:10 instead of 3:20.
    D
    Marco used the wrong hour, getting 2:20 instead of 3:20.
    Show the answer and how to solve it

    The correct choice is the no-error statement: Marco's calculation is correct. Subtracting 25 minutes from 3:45 gives 3:20, which matches exactly what Marco said.

    1. 1The activity lasted 25 minutes from start to finish. To find the start time, go back 25 minutes from the finish time, 3:45. This means subtract 25 minutes.
    2. 2Since 25 is not greater than 45, no borrowing is needed. Subtract the minutes: 45−25=2045 - 25 = 20. The correct start time is 3:20.
    3. 3Compare Marco's stated answer to the correct start time. Marco said 3:20, and the correct start is 3:20. They match exactly, so Marco's calculation is correct.
    4. 4Check the other choices. The add-error formula gives 3:45+25=445 + 25 = 4:10, not 3:20. The wrong-hour error gives 2:20, not 3:20. The hour-subtraction error gives 2:45, not 3:20. None of those errors fit — Marco's answer really is right. The no-error statement is the correct choice.

    Common mistake. A common mistake is assuming there must be an error and overlooking that 3:45−25=345 - 25 = 3:20 really is correct.

    The idea underneath. When the duration is small enough, subtract the minutes only — the hour stays the same.