Estimation and Rounding Off

This chapter will introduce the concept of estimation maths or to students. Also, they will learn about overestimation and underestimation and the uses of estimation in real life.
From this learning concept; students will learn to:

• Apply the estimated weight, height and volume
• To use the concept of estimation in daily life to make calculations easier.

The concept is explained to class 3 students using examples, illustrations and concept maps. At the end of the page, two printable worksheets of estimates with solutions are attached for the students.

Download the worksheets and the printable solutions and assess your knowledge.

What Is Estimation?

• Estimate means to find something close to the correct answer.
• To write the estimated value, we use the squiggly equal sign.“ ~”
• Estimation is helpful in both math and real life.

Estimation Math

• To estimate the numbers of any object or animal, it is not necessary to guess the exact number.
• Estimation is to find a number that is close enough to the exact count.

Let us discuss with an example.

Examples: Guess the number of the fish in the picture.

Answer:

Overestimation and Underestimation

• As estimating numbers are always dependent on guessing, so the estimated number won’t match the exact count often.
• When the estimated number is higher than the exact count, we call it overestimated.
• When the estimated number is lower than the exact count, we call it underestimated.

Let us discuss with an example.

Examples:

(i) A restaurant serves idli to 24 adults and 13 children. Each person will eat at least two idlis. They will have to make

a)50   b) 80   c) 60   d) 100

Answer:The estimated value is 80.

But the exact count is 24 × 2 + 13 × 2 = 74, which is close to 70.

Hence, the value is underestimated.

(ii) Soumya drove his motorcycle 300 miles on Friday, 105 miles on Saturday and 265 miles on Sunday. which of the below number of miles is the best estimate of the number of miles he drove over 3 days?

a) 500 miles   b) 800 miles   c) 600 miles   d) 100 miles

Answer:The estimated number should be 600 miles.

Now, 300 + 105 + 265 = 670 miles

Hence, the number is overestimated.

Estimation of Weights

• To estimate the weight of some object one needs to compare it with some familiar object.
• In order to do this, we should understand some common units of weight measurement.
• For lighter objects, we use gram.
• For heavier objects, we use kilograms.

Let us discuss with an example.

Examples:

The weight of watermelon is almost equal to 20-24 large tomatoes. How many tomatoes can balance the weight of a half watermelon? Estimate the weight of each large tomato?

Answer:

Half of the watermelon will be measured around 10-15 large tomatoes. A watermelon weighs around 2 kg. Then large tomatoes will be weighed around 100 - 150 grams.

Estimation of Heights

• To estimate the height of some object one needs to compare it with some familiar object.
• In order to do this, we should understand some common units of height measurement.
• For shorter lengths, we use centimeters or millimeter.
• For longer lengths, we use kilometers, meters.

Let us discuss with an example.

Examples:

The length of a saree is around 12-14 arm length. Estimate the length of two sarees?

Answer:
The length of the saree is 12-14 arms long. Two sarees will be almost 24-28 arms long. The length of each arm is 60-65 cm. So, the length of each saree is 600-650 cm long. Clearly, length of two sarees will be 1.2-1.5 meters long.

Estimation of Volume

• To estimate the volume of some object one needs to compare it with the volume of some familiar object.
• In order to do this, we should understand some common units that we use to measure volume.
• For a smaller amount of volume, we use millilitre (mL).
• For a larger amount of volume, we use Liter.

Let us discuss with an example.

Examples: A bucket is filled with 5-6 jugs of water. Find how much water is needed to fill half of the bucket.

Answer: A bucket is filled with 5-6 jugs of water. then to fill half of the bucket one will need 2-3 jugs of water. A jug contains almost 1-1.5 liters of water. Hence a bucket must have 5-8 liters of water.

Use of Estimation in real life

• To quickly guess the number of any object.
• Estimation helps us to save time.
• Estimation is used in real life. Like we estimate the number of people coming to any festival. The amount of food or drink, required for a meal.