Estimation is the act of making a careful guess or approximate judgment about the size, amount,
distance, weight, time, or cost of something without measuring exactly. It gives a quick idea of
the actual value and helps to check the reasonableness of exact calculations.
Importance of Estimation
- Provides a quick idea of an answer before detailed calculation.
- Useful when exact measurement is difficult or unnecessary.
- Helps to check whether detailed calculations or results are reasonable.
- Helpful when measuring tools or instruments are not available.
APPLICATION OF ESTIMATION TO DIFFERENT AREAS OF LIVES
- Builders guess how much cement, sand, and bricks they need before building a house.
- Shoppers guess the total cost of items in a shop before paying at the counter.
- Cooks guess the amount of salt, water, or oil when there is no measuring cup.
- Travellers guess how long a journey will take and how far it is before leaving home.
- People guess how much water to drink or how many calories they burn when exercising.
- Party planners guess how many chairs, tables, or plates of food they need for a party.
- Business people guess how much money they will earn or spend in the future.
- Farmers guess how many seeds to plant or how much crop they will harvest.
- Students guess how much time they need to read or finish their homework.
- Families guess how much water is needed to wash clothes or how long it takes to cook food.
Major Areas of Estimation
Estimation can be applied in many real-life situations.
1. Estimation of Dimensions and Distances
Dimensions: length, width, height of objects such as doors, rooms, tables.
Distances: how far two places are apart, e.g. from school gate to the classroom.
Units and Conversions
- 10 mm = 1 cm
- 100 cm = 1 m
- 1,000 m = 1 km
Methods
- Use crude or non-standard measures (pace, cubit, handspan).
- Compare with familiar reference objects (e.g. knowing a door is about 2 m high).
- Round numbers to convenient figures.
- Take several guesses and average them.
Examples
- Estimate the length of the classroom in metres by pacing, then check with a tape.
- Estimate the distance from your house to the nearest shop before measuring it with an odometer.
2. Estimation of Capacity and Mass of Objects
Capacity / Volume: amount of space a container can hold.
Mass: how heavy an object is (amount of matter in it).
Units and Conversions
- Capacity: millilitre (mL), litre (L); 1,000 mL = 1 L.
- Volume: cubic centimetre (cm³), cubic metre (m³); 1,000 cm³ = 1 L.
- Mass: gram (g), kilogram (kg), tonne; 1,000 g = 1 kg.
Methods
- Approximate the container’s shape to a cube, box, or cylinder and compute roughly.
- Compare with known volumes or known weights.
- Round to the nearest convenient unit.
Examples
-
A box 30 cm × 20 cm × 10 cm has estimated volume:
30 × 20 × 10 = 6,000 cm³ ≈ 6 L.
- If a jug holds about 1 L of water, a similar jug will hold about the same.
- 1 L of water has a mass of roughly 1 kg, so 5 L ≈ 5 kg.
3. Estimation of Other Things (Age, Time, Cost, etc.)
- Age: Guessing someone’s age by appearance, e.g. “My teacher is about 40 years old.”
- Time: Estimating how long it takes to complete a task or travel somewhere.
Time conversions: 60 s = 1 min; 60 min = 1 h.
- Cost or Money: Estimating the total cost of items before paying.
- Other Measures: such as area or square roots in simple problems.
Examples
- Estimate that walking from home to school will take about 20 minutes.
- Estimate total cost: 47 notebooks at ₦95 each ≈ 50 × ₦100 = ₦5,000.
4. Quantitative Reasoning Involving Estimation
Quantitative reasoning means applying numerical thinking to real situations. Estimation is a key
tool for:
- Simplifying calculations by rounding numbers.
- Checking accuracy of detailed calculations.
- Making quick decisions when only an approximate figure is needed.
Examples
-
A car travels 138 km in 2 h 15 min.
Approximate 2 h 15 min ≈ 2.25 h, 138 km ≈ 140 km.
Estimated average speed ≈ 140 ÷ 2.25 ≈ 62 km/h.
-
Painting a wall of about 3 m by 4.5 m:
Estimate area ≈ 3 × 4.5 = 13.5 m² ≈ 14 m².
General Techniques for Good Estimation
- Decide what quantity you are estimating (length, time, mass, cost, etc.).
- Choose suitable units for that quantity.
- Use a rough reference (pace, known object, familiar time interval).
- Round or approximate numbers for easier mental calculation.
- If possible, measure later and compare to see how close your estimate is.
- Reflect and adjust future estimates based on experience.
Common Sources of Error
- Inconsistent crude measures (e.g. paces of different lengths).
- Wrong or unsuitable units.
- Guessing without any reference point.
- Forgetting to check estimates against actual measurements.
