Reference / Curriculum / 3B / Chapter 14

3B · Chapter 14 · Lesson 5

Calculating Time — Part 4

Solve multi-event schedules with separate intervals and clear units.

MATH-3B-C14-L06Independent and tutor-supported

Today's mathematical question

A student leaves at 6:30 a.m., walks 15 minutes, then studies 55 minutes. At what time does studying end?

Learning target

Solve multi-event schedules with separate intervals and clear units.

Before starting: Prior lesson: Calculating Time — Part 3. Try the warm-up independently.

Prerequisite · 3 questions

Check earlier skills first

These are earlier ideas you need for today; revisit them if they are difficult.

  1. P1

    How many minutes pass from 11:40 p.m. to 1:55 a.m.?

    Reveal explanation

    Answer: 135 min

    Count from 11:40 p.m. to the next whole hour, then onward to 1:55 a.m.. The intervals add to 135 minutes.

    Analog clock showing 11:40 p.m..
  2. P2

    How many minutes pass from 11:15 p.m. to 11:50 p.m.?

    Reveal explanation

    Answer: 35 min

    Count from 11:15 p.m. to the next whole hour, then onward to 11:50 p.m.. The intervals add to 35 minutes.

    Analog clock showing 11:15 p.m..
  3. P3

    How many minutes pass from 10:50 a.m. to 12:20 p.m.?

    Reveal explanation

    Answer: 90 min

    Count from 10:50 a.m. to the next whole hour, then onward to 12:20 p.m.. The intervals add to 90 minutes.

    Analog clock showing 10:50 a.m..

Learn and understand

Multi-event time problems require a timeline with more than one segment. Add walking time first, then time spent at the activity, without applying the second duration to the original start. Check whether the final time belongs to the same day. A journey might contain a 20-minute walk and a 45-minute class. Find the end of each activity in order. A timeline keeps the intermediate times visible.

Represent it three ways

  1. Concrete: Build equal pieces, measures, counters or shapes with real objects when useful.
  2. Pictorial: Draw one arrow per event; label intermediate arrival time, then add the next duration and mark the final finish.
  3. Abstract: Write the matching number sentence, calculation, comparison or mathematical description. Explain each number's unit.

Important vocabulary

timeline
ordered diagram of events
intermediate time
time between stages
duration
length of each stage

Fully worked examples and checks

Try each new understanding check before revealing the explanation.

Worked example 1

Explore, calculate, verify

A student leaves at 6:30 a.m., walks 15 minutes, then studies 55 minutes. At what time does studying end?

Analog clock showing 6:30 a.m..
  1. Identify the whole, the units, and what the question asks.
  2. First reach 6:45 a.m. after walking, then add 55 minutes. Finish at 7:40 a.m..
  3. Check that the answer uses the right units and makes sense.

Answer: 7:40 a.m.

Check your understanding 1

A student leaves at 11:20 a.m., walks 25 minutes, then studies 35 minutes. At what time does studying end?

Reveal answer and explanation

12:20 p.m. — First reach 11:45 a.m. after walking, then add 35 minutes. Finish at 12:20 p.m..

Analog clock showing 11:20 a.m..

Worked example 2

Explore, calculate, verify

A student leaves at 7:50 a.m., walks 15 minutes, then studies 55 minutes. At what time does studying end?

Analog clock showing 7:50 a.m..
  1. Identify the whole, the units, and what the question asks.
  2. First reach 8:05 a.m. after walking, then add 55 minutes. Finish at 9:00 a.m..
  3. Check that the answer uses the right units and makes sense.

Answer: 9:00 a.m.

Check your understanding 2

A student leaves at 6:00 a.m., walks 15 minutes, then studies 45 minutes. At what time does studying end?

Reveal answer and explanation

7:00 a.m. — First reach 6:15 a.m. after walking, then add 45 minutes. Finish at 7:00 a.m..

Analog clock showing 6:00 a.m..

Worked example 3

Explore, calculate, verify

A student leaves at 10:25 a.m., walks 20 minutes, then studies 55 minutes. At what time does studying end?

Analog clock showing 10:25 a.m..
  1. Identify the whole, the units, and what the question asks.
  2. First reach 10:45 a.m. after walking, then add 55 minutes. Finish at 11:40 a.m..
  3. Check that the answer uses the right units and makes sense.

Answer: 11:40 a.m.

Check your understanding 3

A student leaves at 10:45 a.m., walks 15 minutes, then studies 55 minutes. At what time does studying end?

Reveal answer and explanation

11:55 a.m. — First reach 11:00 a.m. after walking, then add 55 minutes. Finish at 11:55 a.m..

Analog clock showing 10:45 a.m..

Guided · 5 questions

Guided practice

Keep the model and earlier examples visible while practising.

  1. G1

    A student leaves at 1:35 p.m., walks 25 minutes, then studies 45 minutes. At what time does studying end?

    Reveal explanation

    Answer: 2:45 p.m.

    First reach 2:00 p.m. after walking, then add 45 minutes. Finish at 2:45 p.m..

    Analog clock showing 1:35 p.m..
  2. G2

    A student leaves at 8:15 a.m., walks 25 minutes, then studies 55 minutes. At what time does studying end?

    Reveal explanation

    Answer: 9:35 a.m.

    First reach 8:40 a.m. after walking, then add 55 minutes. Finish at 9:35 a.m..

    Analog clock showing 8:15 a.m..
  3. G3

    A student leaves at 8:25 a.m., walks 15 minutes, then studies 35 minutes. At what time does studying end?

    Reveal explanation

    Answer: 9:15 a.m.

    First reach 8:40 a.m. after walking, then add 35 minutes. Finish at 9:15 a.m..

    Analog clock showing 8:25 a.m..
  4. G4

    A student leaves at 3:00 p.m., walks 15 minutes, then studies 35 minutes. At what time does studying end?

    Reveal explanation

    Answer: 3:50 p.m.

    First reach 3:15 p.m. after walking, then add 35 minutes. Finish at 3:50 p.m..

    Analog clock showing 3:00 p.m..
  5. G5

    A student leaves at 5:00 p.m., walks 25 minutes, then studies 55 minutes. At what time does studying end?

    Reveal explanation

    Answer: 6:20 p.m.

    First reach 5:25 p.m. after walking, then add 55 minutes. Finish at 6:20 p.m..

    Analog clock showing 5:00 p.m..

Independent · 8 questions

Independent practice

Work these without hints and explain the method used. Write answers on paper.

  1. I1

    A student leaves at 1:50 p.m., walks 20 minutes, then studies 35 minutes. At what time does studying end?

    Reveal explanation

    Answer: 2:45 p.m.

    First reach 2:10 p.m. after walking, then add 35 minutes. Finish at 2:45 p.m..

    Analog clock showing 1:50 p.m..
  2. I2

    A student leaves at 10:15 a.m., walks 20 minutes, then studies 45 minutes. At what time does studying end?

    Reveal explanation

    Answer: 11:20 a.m.

    First reach 10:35 a.m. after walking, then add 45 minutes. Finish at 11:20 a.m..

    Analog clock showing 10:15 a.m..
  3. I3

    A student leaves at 1:25 p.m., walks 20 minutes, then studies 55 minutes. At what time does studying end?

    Reveal explanation

    Answer: 2:40 p.m.

    First reach 1:45 p.m. after walking, then add 55 minutes. Finish at 2:40 p.m..

    Analog clock showing 1:25 p.m..
  4. I4

    A student leaves at 2:00 p.m., walks 25 minutes, then studies 35 minutes. At what time does studying end?

    Reveal explanation

    Answer: 3:00 p.m.

    First reach 2:25 p.m. after walking, then add 35 minutes. Finish at 3:00 p.m..

    Analog clock showing 2:00 p.m..
  5. I5

    A student leaves at 1:00 p.m., walks 15 minutes, then studies 55 minutes. At what time does studying end?

    Reveal explanation

    Answer: 2:10 p.m.

    First reach 1:15 p.m. after walking, then add 55 minutes. Finish at 2:10 p.m..

    Analog clock showing 1:00 p.m..
  6. I6

    A student leaves at 11:40 a.m., walks 25 minutes, then studies 55 minutes. At what time does studying end?

    Reveal explanation

    Answer: 1:00 p.m.

    First reach 12:05 p.m. after walking, then add 55 minutes. Finish at 1:00 p.m..

    Analog clock showing 11:40 a.m..
  7. I7

    A student leaves at 4:40 p.m., walks 15 minutes, then studies 35 minutes. At what time does studying end?

    Reveal explanation

    Answer: 5:30 p.m.

    First reach 4:55 p.m. after walking, then add 35 minutes. Finish at 5:30 p.m..

    Analog clock showing 4:40 p.m..
  8. I8

    A student leaves at 10:20 a.m., walks 15 minutes, then studies 35 minutes. At what time does studying end?

    Reveal explanation

    Answer: 11:10 a.m.

    First reach 10:35 a.m. after walking, then add 35 minutes. Finish at 11:10 a.m..

    Analog clock showing 10:20 a.m..

Challenge · 2 questions

Challenge and error analysis

Go beyond arithmetic: justify a claim, correct reasoning, or connect two representations.

  1. C1

    Explain how 11:40 a.m. plus 30 minutes crosses noon. At what time does it finish?

    Reveal explanation

    Answer: 12:10 p.m.

    20 minutes reach noon; then 10 more minutes reach 12:10 p.m.

  2. C2

    A trip begins at 11:35 p.m. and lasts 35 minutes. On which day does it finish and at what time?

    Reveal explanation

    Answer: Next day at 12:10 a.m.

    25 minutes reach midnight; 10 minutes more reach 12:10 a.m. on the next day.

Exit · 3 questions

Exit check

Solve independently, then return on another day to check retention.

  1. E1

    A student leaves at 1:35 p.m., walks 15 minutes, then studies 35 minutes. At what time does studying end?

    Reveal explanation

    Answer: 2:25 p.m.

    First reach 1:50 p.m. after walking, then add 35 minutes. Finish at 2:25 p.m..

    Analog clock showing 1:35 p.m..
  2. E2

    A student leaves at 7:55 a.m., walks 25 minutes, then studies 55 minutes. At what time does studying end?

    Reveal explanation

    Answer: 9:15 a.m.

    First reach 8:20 a.m. after walking, then add 55 minutes. Finish at 9:15 a.m..

    Analog clock showing 7:55 a.m..
  3. E3

    A student leaves at 4:10 p.m., walks 15 minutes, then studies 35 minutes. At what time does studying end?

    Reveal explanation

    Answer: 5:00 p.m.

    First reach 4:25 p.m. after walking, then add 35 minutes. Finish at 5:00 p.m..

    Analog clock showing 4:10 p.m..
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