Use seconds as a unit of time

What you will learn

• Use seconds as a unit of time

Models used: number sentences, stories, tables.

Before you start

• Convert between hours and minutes

Sixty seconds make one minute

A timer runs for 2 minutes and 15 seconds. How many seconds pass altogether?

1. The whole bar is one minute. Each section is ten seconds.

   Seconds measure short stretches of time. Six groups of ten seconds make one minute.

   60 s = 1 min

   60

   1010 s1010 s1010 s1010 s1010 s1010 s

2. The complete bar is the whole. Each labelled section is one part of it.

   Our timer runs for two whole minutes first. Each minute contains 60 seconds.

   2 × 60 = 120 s

   120

   60first minute60second minute

3. The complete bar is the whole. Each labelled section is one part of it.

   The extra 15 seconds are already in seconds. Add them to the 120.

   120 + 15 = 135 s

   135

   6060 s6060 s1515 s

4. The same duration in two forms. Read each value with the heading above its column.

   Check by taking out two complete groups of 60. We get two minutes, with 15 seconds left.

   135 s = 2 min 15 s

   The same duration in two forms

   Minutes	Extra seconds	Total seconds
   2	15	135

Worked example: A new example, together

Convert 3 min 36 s to seconds.

1. Convert the minutes, then add the extra seconds. Read each value with the heading above its column.

   Keep complete units and extra units separate until their names match.

   Each minute contains 60 seconds. Convert the whole minutes first, then add the seconds already given.

   Convert the minutes, then add the extra seconds

   Whole minutes	Extra seconds
   3	36

2. Convert the minutes, then add the extra seconds. Read each value with the heading above its column.

   Each minute is 60 seconds.

   Convert the minutes, then add the extra seconds

   Whole minutes	Extra seconds
   3	36

   Convert 3 min 36 s to seconds.

   216 seconds

3. Convert the minutes, then add the extra seconds. Read each value with the heading above its column.

   3 × 60 = 180.

   Convert the minutes, then add the extra seconds

   Whole minutes	Extra seconds
   3	36

4. Convert the minutes, then add the extra seconds. Read each value with the heading above its column.

   180 + 36 = 216 seconds.

   Convert the minutes, then add the extra seconds

   Whole minutes	Extra seconds
   3	36

5. Convert the minutes, then add the extra seconds. Read each value with the heading above its column.

   Check the result against the question we started with.

   216 seconds splits into 3 groups of 60 and 36 left.

   We found 216 seconds. Each minute contains 60 seconds. Convert the whole minutes first, then add the seconds already given.

   Convert the minutes, then add the extra seconds

   Whole minutes	Extra seconds
   3	36

Common mistakes to discuss

• The hundred-second minute. A minute holds 60 seconds, so 1 min 15 s is 75 s.

Check your understanding

• Use seconds as a unit of time
• rename a duration without changing how long it lasts
• check the answer against the original quantities and units

Explain your reasoning to an adult, then try a fresh question in the interactive lesson. A result from one attempt is not proof of lasting mastery.