Length: km, m, cm, mm
You walk 500 m to school, a pencil is 15 cm long and the road to the next city is 40 km. We choose a unit that fits the thing we measure.
The units of length are kilometre (km), metre (m), centimetre (cm) and millimetre (mm). 1 km = 1,000 m, 1 m = 100 cm, 1 cm = 10 mm.
In the figure : Moving to a smaller length unit we multiply by 1000, 100 or 10.
Rule 1: Bigger to smaller: multiply — Multiply by 1000, 100 or 10.
- Easy : 3 km = 3 × 1,000 = 3,000 m.
- Medium : 3 km 250 m = 3,000 + 250 = 3,250 m.
- Exam-type : 2 m 5 cm = 200 + 5 = 205 cm (the 5 cm is not 50).
Rule 2: Smaller to bigger: divide — Divide by 1000, 100 or 10.
- Easy : 350 cm = 3.5 m.
- Medium : 6,500 m = 6.5 km and 45 mm = 4.5 cm.
- Exam-type : Compare 1.2 m, 110 cm, 1 m 15 cm: 120, 110, 115 cm. Order: 110 < 115 < 120.
Length: km, m, cm, mm
In the app you can move this figure with your finger.
Open in the appChoose a sensible unit: an ant in mm, a pencil in cm, a room in m, a city distance in km.
Comparing 150 cm and 2 m by looking at 150 > 2. Change both to cm first.
Memory clue: km → m → cm → mm, steps of ×1000, ×100, ×10.
Spot the difference
| Unit | Equal to |
|---|---|
| 1 km | 1,000 m |
| 1 m | 100 cm |
| 1 cm | 10 mm |
Practice questions
- 1Change 3 km to metres.
- 2Change 4 m to centimetres.
- 3Change 7 cm to millimetres.
- 4Change 6,500 m to km.
- 5Change 3 km 250 m to metres.
- 6Change 2 m 5 cm to centimetres.
- 7Arrange from smallest: 1.2 m, 110 cm, 1 m 15 cm.
- 8Meena says 150 cm is longer than 2 m because 150 > 2. What is wrong?
Show answers (try them yourself first)
- 13,000 m
- 2400 cm
- 370 mm
- 46.5 km
- 53,250 m
- 6205 cm
- 7110 cm, 1 m 15 cm, 1.2 m
- 8The units are different. 2 m = 200 cm, so 2 m is longer.
Weight: tonne, quintal, kg, g
A shopkeeper weighs sugar in kg, a pinch of salt is in grams, and a truck carries goods in tonnes. Weight has different units for light and heavy things.
1 tonne = 1,000 kg, 1 quintal = 100 kg, 1 kg = 1,000 g. Bigger to smaller: multiply. Smaller to bigger: divide.
In the figure : Weight units and how they are linked.
Rule 1: Bigger to smaller — Multiply by 1,000 or 100.
- Easy : 2 kg = 2 × 1,000 = 2,000 g.
- Medium : 4 quintal = 4 × 100 = 400 kg.
- Exam-type : 3 kg 250 g = 3,000 + 250 = 3,250 g.
Rule 2: Smaller to bigger — Divide by 1,000 or 100.
- Easy : 2,500 g = 2 kg 500 g.
- Medium : 750 kg = 7.5 quintal.
- Exam-type : A bag holds 25 kg. How many bags make 1 tonne? 1,000 ÷ 25 = 40 bags.
Weight: tonne, quintal, kg, g
In the app you can move this figure with your finger.
Open in the appA tonne is a very large weight. 1 tonne = 10 quintals.
Confusing quintal (100 kg) with tonne (1,000 kg).
Memory clue: Kilo = thousand grams; quintal = hundred kilos; tonne = thousand kilos.
Spot the difference
| Unit | Equal to |
|---|---|
| 1 kg | 1,000 g |
| 1 quintal | 100 kg |
| 1 tonne | 1,000 kg |
Practice questions
- 1Change 2 kg to grams.
- 2Change 4 quintal to kg.
- 3Change 3 tonne to kg.
- 4Change 2,500 g to kg and g.
- 5Change 750 kg to quintal.
- 6Change 3 kg 250 g to grams.
- 7A bag holds 25 kg. How many bags make 1 tonne?
- 8A farmer says 20 quintal is 2 tonne. Is he right? Explain.
Show answers (try them yourself first)
- 12,000 g
- 2400 kg
- 33,000 kg
- 42 kg 500 g
- 57.5 quintal
- 63,250 g
- 71,000 ÷ 25 = 40 bags
- 8Yes. 20 quintal = 20 × 100 = 2,000 kg = 2 tonne.
Capacity: litre and millilitre
Milk comes in litres and a spoon of medicine is in millilitres. The amount a container holds is its capacity.
1 litre (L) = 1,000 millilitres (ml). Litre to ml: multiply by 1,000. ml to litre: divide by 1,000.
In the figure : Four 250 ml bottles together make 1,000 ml = 1 litre.
Rule 1: Litre and millilitre — Multiply by 1,000 or divide by 1,000.
- Easy : 3 L = 3,000 ml and 500 ml = 0.5 L.
- Medium : 1.2 L = 1,200 ml and 2,500 ml = 2 L 500 ml.
- Exam-type : 5 bottles of 200 ml = 5 × 200 = 1,000 ml = 1 L.
Rule 2: How many small containers? — Divide the big capacity by the small capacity in the same unit.
- Easy : 2,000 ml ÷ 250 ml = 8 cups.
- Medium : 1,500 ml ÷ 400 ml = 3 glasses and 300 ml left.
- Exam-type : 3 bottles of 1.5 L = 3 × 1.5 = 4.5 L = 4,500 ml.
Capacity: litre and millilitre
In the app you can move this figure with your finger.
Open in the appAlways write the same unit before you divide.
Writing 0.75 L as 75 ml. It is 750 ml.
Memory clue: Litre = 1,000 ml, like kg = 1,000 g.
Spot the difference
| Unit | Equal to |
|---|---|
| 1 L | 1,000 ml |
| 500 ml | 0.5 L |
| 250 ml | 0.25 L |
Practice questions
- 1Change 3 L to ml.
- 2Change 500 ml to litres.
- 3Change 1.2 L to ml.
- 4Change 2,500 ml to L and ml.
- 5How many 250 ml cups fill a 2 L jug?
- 6A 1,500 ml jug fills glasses of 400 ml. How many full glasses and how much is left?
- 73 bottles of 1.5 L each are bought. How many litres and how many ml is that?
- 8Ravi writes 0.75 L = 75 ml. Correct him.
Show answers (try them yourself first)
- 13,000 ml
- 20.5 L
- 31,200 ml
- 42 L 500 ml
- 52,000 ÷ 250 = 8 cups
- 63 glasses and 300 ml left.
- 74.5 L = 4,500 ml
- 80.75 × 1,000 = 750 ml.
Adding and subtracting measures
A tailor adds 2 m 70 cm and 1 m 60 cm of ribbon. He first adds the cm, then the metres. When the cm reach 100, they become a metre.
To add or subtract measures, write the same units in the same column. Work with the smaller unit first. If the smaller unit reaches 100 cm or 1,000 g or 1,000 ml, change it to the bigger unit.
In the figure : 3 m 45 cm + 2 m 80 cm: 125 cm is carried as 1 m 25 cm, so the answer is 6 m 25 cm.
Rule 1: Adding measures — Add the small unit, carry to the bigger unit, then add the bigger unit.
- Easy : 3 m 45 cm + 2 m 80 cm = 5 m 125 cm = 6 m 25 cm.
- Medium : 4 kg 600 g + 2 kg 700 g = 6 kg 1,300 g = 7 kg 300 g.
- Exam-type : 2 km 600 m + 1 km 700 m = 3 km 1,300 m = 4 km 300 m.
Rule 2: Subtracting measures — If the top small unit is smaller, borrow from the bigger unit, or change all to the small unit.
- Easy : 6 m − 2 m 40 cm = 600 − 240 = 360 cm = 3 m 60 cm.
- Medium : 3 kg 200 g − 1 kg 500 g = 3,200 − 1,500 = 1,700 g = 1 kg 700 g.
- Exam-type : 7 m 20 cm − 3 m 85 cm = 720 − 385 = 335 cm = 3 m 35 cm.
Add and subtract the small unit first, in its own column.
Writing 5 m 125 cm as the final answer. 125 cm is more than 1 m; carry it.
Memory clue: Small unit first, carry at 100 or 1,000.
Spot the difference
| Step | What to do |
|---|---|
| 1 | Write units in columns |
| 2 | Work on the small unit |
| 3 | Carry or borrow, then big unit |
Practice questions
- 1Add: 3 m 45 cm + 2 m 80 cm.
- 2Add: 4 kg 600 g + 2 kg 700 g.
- 3Add: 5 L 300 ml + 2 L 450 ml.
- 4Subtract: 6 m − 2 m 40 cm.
- 5Subtract: 3 kg 200 g − 1 kg 500 g.
- 6Subtract: 5 L − 1 L 250 ml.
- 7Add: 2 km 600 m + 1 km 700 m.
- 8Subtract 7 m 20 cm − 3 m 85 cm and check by adding.
Show answers (try them yourself first)
- 16 m 25 cm
- 27 kg 300 g
- 37 L 750 ml
- 43 m 60 cm
- 51 kg 700 g
- 63 L 750 ml
- 74 km 300 m
- 83 m 35 cm. Check: 3 m 35 cm + 3 m 85 cm = 7 m 20 cm.
Word problems on measures
A tailor needs 1 m 50 cm of cloth for one shirt and wants to stitch 3 shirts. How much cloth should he buy? This is a word problem on measures.
Steps: (1) read and find what is given and what is asked, (2) make all units the same, (3) choose the operation, (4) solve, (5) check if the answer is sensible.
In the figure : A 30 m rope cut into 5 m pieces gives 30 ÷ 5 = 6 pieces.
Rule 1: Equal groups — Equal groups together: multiply. Sharing or cutting into equal pieces: divide.
- Easy : 5 packets of 2 kg = 5 × 2 = 10 kg.
- Medium : 3 shirts of 1 m 50 cm = 3 × 150 = 450 cm = 4 m 50 cm.
- Exam-type : 30 m rope ÷ 5 m = 6 pieces.
Rule 2: Price and speed — Rate × quantity = total.
- Easy : ₹ 36 per kg × 4 kg = ₹ 144.
- Medium : 12 km per litre × 5 litres = 60 km.
- Exam-type : 5 kg sugar − 1 kg 750 g used = 5,000 − 1,750 = 3,250 g = 3 kg 250 g left.
Finish by asking: is the answer sensible? A shirt cannot need 50 m of cloth.
Mixing units, like adding 2 kg and 500 g as 502. Change to g or kg first.
Memory clue: Read – same unit – sign – solve – sense check.
Spot the difference
| Problem type | Use |
|---|---|
| Equal groups | × |
| Cutting into pieces | ÷ |
| Rate and total | × |
Practice questions
- 15 packets of 2 kg each. How many kg in all?
- 2A 30 m rope is cut into 5 m pieces. How many pieces?
- 3Sugar costs ₹ 36 per kg. Find the cost of 4 kg.
- 4A scooter runs 12 km on 1 litre. How far on 5 litres?
- 5A tailor needs 1 m 50 cm for one shirt. How much cloth for 3 shirts?
- 6A jug of 2 L fills glasses of 250 ml. How many glasses?
- 75 kg sugar is bought and 1 kg 750 g is used. How much is left?
- 8A tank holds 5 L 500 ml. Eight glasses of 250 ml are taken out. How much water is left?
Show answers (try them yourself first)
- 110 kg
- 230 ÷ 5 = 6
- 3₹ 144
- 460 km
- 54 m 50 cm
- 62,000 ÷ 250 = 8
- 73 kg 250 g
- 88 × 250 = 2,000 ml = 2 L. Left: 5 L 500 ml − 2 L = 3 L 500 ml.