Grade 3 (age 8-9)

Length & Time

Picking the right unit makes a length easier to measure. Small things use millimeters or centimeters and big things use meters or kilometers. A clock shows hours with its short hand and minutes with its long hand. Slide to change the length, then move the clock hands to read the time.

Let's Measure Length

📏 Length Units

①Very short → mm (millimeter)

②Pencils, books → cm (centimeter)

③Classroom, playground → m (meter)

④1cm = 10mm, 1m = 100cm

Measure with a Ruler

Length (cm)8

💡 How to Measure Length

①Align start with 0 on the ruler

②Read the mark at the end point

③Small marks between cm = mm

Reading a Clock

Hour3

Minute30

⏰ How to Read a Clock

①Short hand (hour) → the hour

②Long hand (minute) → the minute

③Minute hand on 12 = on the hour

④1 hour = 60 min, 1 min = 60 sec

Summary

Length Conversion

1m = 100cm = 1000mm

Big → small: ×10, ×100

Time Conversion

1 hour = 60 min, 1 min = 60 sec

Time bundles in 60s

A Day

1 day = 24 hours

AM 12 hours + PM 12 hours

🎯 Key Points

①Length: mm < cm < m < km

②1cm = 10mm, 1m = 100cm

③Clock: short = hour, long = minute

④1 hour = 60 min, 1 day = 24 hours

⑤Watch units carefully when converting

Examples and Unit Test

Example 1

How many mm is 3 cm?

1 cm = 10 mm.

3 cm = 3 × 10 = 30 mm.

▸ 30 mm

To convert cm to mm, multiply by 10.

Example 2

How many m and cm is 250 cm?

Since 1 m = 100 cm, see how many 100s fit in 250 cm.

250 = 200 + 50, so it is 2 m 50 cm.

▸ 2 m 50 cm

Group every 100 cm into 1 m and write it as m and cm.

Unit Test

How many cm is 1 m?

①10 cm

②100 cm

③1000 cm

④60 cm

▸ ② 100 cm

The length-unit relationship is 1 m = 100 cm.

So 1 m = 100 cm.

← Previous

Plane Figures

Big Numbers