Lesson 8- Rounding Decimals

Objective:

At the end of this lesson, students should be able to round decimals to the nearest whole number, tenth, hundredth or thousandth.

When you round a decimal, you represent it by a number that the decimal is closest to. Rounding enables you to write a number in a way that suits your purpose. Decimals can be rounded to the nearest whole number, tenth, hundredth, thousandth, etc.

Steps to follow when rounding decimals:

Quick reminder:

From previous knowledge acquired on the study of decimal number lines;

6.5 is half way between 6 and 7

6.54 is nearer to 7, because it is more than half way between 6 and 7.

6.49 is nearer to 6, because it is less than half way between 6 and 7.

6.501 is more than half way between 6 and 7.

6.498 is less than half way between 6 and 7.

Suppose we are to round these decimals the nearest whole number;

A similar approach is applied when rounding numbers.

Example 1

Round these numbers to their nearest whole number

a) 7.49 b) 18.91 c) 39.085

Example 2

Round to 1 decimal place (nearest tenth).

a)0.455 b) 8.99 c) 57.08

Solution

Example 3

Round to the nearest hundredth (2 decimal places)

a) 49.894 b) 12.899 c) 130.007

Solution

Example 4

Round to the nearest thousandth (3 decimal places)

a) 99.9985 b) 18.9063

Solution

Unit 10 Lesson 8: Exercise 1

Round these decimals to the nearest whole number.

1) 5 2) 6 3) 18 4) 0 5) 29
6) 100 7) 1 8) 62 9) 100 10) 433

Unit 10 Lesson 8: Exercise 2

Round to the nearest tenth.

1) 0.5 2) 3.1 3) 16.0 4) 39.9 5) 8.4
6) 0.1 7) 48.0 8) 100.0 9) 162.4 10) 840.4

Unit 10 Lesson 8: Exercise 3

Round these decimal numbers to 2 decimal places.

1) 0.24 2) 6.08 3) 3.45 4) 62.81 5) 74.44
6) 13.40 7) 46.93 8) 10.11 9) 209.50 10) 466.65

Unit 10 Lesson 8: Exercise 4

Round these to the nearest 1/1000 of a kilometer.

1) 4.377km   2) 27.242km   3) 57.702km   4) 46.278km
5) 0.129km   6) 11.230km   7) 38.384km   8) 851.227km
9) 51.500km   10) 250.635km

Unit 10 Lesson 8: Exercise 5

Write the decimal equivalent to each fraction to the nearest hundredth.

1) 0.29   2) 0.63   3) 0.55   4) 0.33
5) 0.42   6) 0.56   7) 0.58   8) 0.22
9) 0.57   10) 0.88

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