**Key Unit Conversions:**
• 1 cm = 10 mm
• 1 m = 100 cm
• 1 km = 1,000 m
**Converting Between Units:**
To convert smaller to larger: divide (e.g., 100 cm ÷ 100 = 1 m)
To convert larger to smaller: multiply (e.g., 1 m × 100 = 100 cm)
**Adding/Subtracting Lengths:**
Step 1: Convert all measurements to the same unit
Step 2: Add or subtract the numbers
Step 3: Convert back if needed (e.g., 1,000 m = 1 km)
**Reading a Scale:**
Start reading from the 0 mark, not from the edge. Count small marks between centimetres for millimetres.
**Diagrams to Remember:**
Scale with millimetre marks — 10 small marks = 1 cm. Double number lines showing multiplication relationships between units.
**Don't Confuse:**
Millimetre is smallest (mm), then centimetre (cm), then metre (m), then kilometre (km) — from tiny to huge. When comparing lengths, ALWAYS convert to the same unit first before using <, =, or > signs.
Q1. How many millimetres are there in 5 centimetres?
Answer: B — Since 1 cm = 10 mm, then 5 cm = 5 × 10 = 50 mm.
Q2. Fill in the blank: 1 kilometre = _______ metres.
Answer: C — By definition from the chapter, 1 km = 1,000 m because kilo means thousand.
Q3. Convert 234 centimetres into millimetres.
Answer: B — To convert cm to mm, multiply by 10: 234 × 10 = 2,340 mm.
Q4. Which is larger: 456 cm or 5 m?
Answer: B — Convert to same unit: 5 m = 500 cm, and 500 cm > 456 cm, so 5 m is larger.
Q5. Saji walked 3 km 450 m in the morning and 4 km 650 m in the evening. How far did he walk in total?
Answer: B — Add km and m separately: 3 + 4 = 7 km, and 450 + 650 = 1,100 m = 1 km 100 m, so total = 8 km 100 m.
Q6. What does 89 mm equal when written in cm and mm?
Answer: A — Since 10 mm = 1 cm, divide: 89 ÷ 10 = 8 remainder 9, so 89 mm = 8 cm 9 mm.
Q7. India Gate is 42 metres tall. How many centimetres is this?
Answer: C — To convert metres to centimetres, multiply by 100: 42 × 100 = 4,200 cm.
Q8. The distance between two buttons on a shirt is 5 cm. How many millimetres is this?
Answer: C — Since 1 cm = 10 mm, multiply: 5 × 10 = 50 mm.
Q9. Which measurement could represent the height of a house?
Answer: C — A typical house is about 15-20 metres tall, so 50 m is a reasonable height for a taller building, while cm and mm are too small and km is far too large.
Q10. Convert 5,792 cm into metres and centimetres.
Answer: A — Divide by 100: 5,792 ÷ 100 = 57 with remainder 92, so 5,792 cm = 57 m 92 cm.
What does 1 mm mean?
1 millimetre is one tenth of a centimetre, used to measure very small things like the thickness of a coin.
How many millimetres are in 1 centimetre?
1 cm = 10 mm (ten millimetres equal one centimetre).
What is the relationship between metre and centimetre?
1 m = 100 cm (one hundred centimetres equal one metre).
What does 1 km equal?
1 km = 1,000 m (one kilometre equals one thousand metres, used for long distances like between cities).
Convert 45 mm to cm and mm.
45 mm = 4 cm 5 mm (because 40 mm = 4 cm and 5 mm remains).
How do you add 3 km 450 m and 4 km 650 m?
Add the kilometres together (3 + 4 = 7 km) and metres together (450 + 650 = 1,100 m), then convert 1,100 m to 1 km 100 m, giving 8 km 100 m.
Convert 6 m 34 cm into only centimetres.
6 m 34 cm = 634 cm (because 6 m = 600 cm, so 600 + 34 = 634 cm).
What tools can measure long distances?
Long tape, rodometer (measuring wheel), rangefinder, and laser distance meter are tools used to measure long distances.
When comparing 456 cm and 5 m, which is larger?
5 m is larger because 5 m = 500 cm, and 500 cm > 456 cm, so 456 cm < 5 m.
What is the total distance of The Vivek Express train journey?
The Vivek Express journey from Dibrugarh to Kanniyakumari is 4,187 km long.
What is 1 millimetre and why do we need it? [1 mark]
1 mm is one tenth of a centimetre, used when measuring very small objects like nails or screws where cm is not precise enough.
Fill in the blanks: (a) 1 m = _____ cm (b) 1 km = _____ m [2 marks]
Use the conversion relationships from the chapter: centimetres are 100 times smaller than metres, and metres are 1,000 times smaller than kilometres.
Explain with an example from your daily life why we need different units of measurement like mm, cm, m, and km. [3 marks]
Use examples such as: mm for measuring the thickness of a coin, cm for measuring pencil length, m for measuring classroom size, and km for measuring distance between cities. Show that using the wrong unit makes measurement confusing.
The Vivek Express train journey has 8 stations listed. Station 1 (Dimapur) is 306 km from Dibrugarh, and Station 8 (Kanniyakumari) is 4,187 km from Dibrugarh. (a) What is the distance between these two stations? (b) If a person travels from Guwahati (556 km) to Visakhapatnam (2,450 km), how far do they travel? (c) Explain how you solved part (b). [5 marks]
Part (a): Subtract the starting distance from the ending distance (4,187 − 306 = 3,881 km). Part (b): Use the same method (2,450 − 556 = 1,894 km). Part (c): Explain that when distances are given from the same starting point, we subtract the smaller from the larger to find the distance between two places.
True or False: 3 km 450 m + 4 km 650 m = 7 km 1,100 m. Explain your answer. [2 marks]
The addition is correct (3 + 4 = 7 km, 450 + 650 = 1,100 m), but the final answer must be simplified because 1,100 m = 1 km 100 m, so the true answer is 8 km 100 m.
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