Seconds, minutes and hours

A blink lasts about a second. A song lasts about 3 minutes. A movie lasts about 2 hours. The three units are connected:

$1 \text{ minute} = 60 \text{ seconds}$ $1 \text{ hour} = 60 \text{ minutes} = 3{,}600 \text{ seconds}$

What is this?

The number 60 is the link. To go from a bigger unit to a smaller unit, multiply by 60. To go from a smaller to a bigger, divide by 60.

• 2 minutes = 2 × 60 = 120 seconds.
• 5 hours = 5 × 60 = 300 minutes.
• 180 seconds = 180 ÷ 60 = 3 minutes.

When time is given in mixed units like "2 hours 30 minutes", we add unit by unit, carrying when the minutes cross 60.

For example, 1 h 45 min + 2 h 30 min:

• min: 45 + 30 = 75 min = 1 h 15 min.
• h: 1 + 2 + 1 = 4 h, with 15 min left.
• Total: 4 h 15 min.

Subtraction works the same way , borrow 1 h = 60 min if needed.

We also use days, weeks, months, years for longer time:

• 1 day = 24 hours.
• 1 week = 7 days.
• 1 year = 12 months ≈ 365 days.

Each day, the hour hand of a clock turns twice round the face (once for AM and once for PM).

Worked examples

Example 1. Convert 4 minutes to seconds.

• 4 × 60 = 240 seconds.

Example 2. Convert 150 minutes to hours and minutes.

• 150 ÷ 60 = 2 with remainder 30.
• 2 hours 30 minutes.

Example 3. Add: 2 h 45 min + 1 h 35 min.

• min: 45 + 35 = 80 min = 1 h 20 min.
• h: 2 + 1 + 1 = 4 h, with 20 min.
• 4 h 20 min.

Try it

1. Convert 3 minutes to seconds.
2. Convert 6 hours to minutes.
3. Convert 240 seconds to minutes.
4. Add: 1 h 50 min + 2 h 25 min.
5. Subtract: 4 h − 1 h 45 min.

Hands-on

One-minute test. Time yourself for one minute. Count how many times you can write your full name in that time. How many words can you read in one minute?

Daily time log. Write down what you do during one day and how long each thing takes , sleep, school, play, eat. Add up the hours. Does it come close to 24?