HOW TO ROUND DECIMALS TO THE NEAREST WHOLE NUMBER

A decimal number contains two parts :

(i) Whole number part

(ii) Decimal part

The decimal point (.) separates the above two parts in a decimal number.

Example :

5.2

In the number above, the whole number part is '5' and the decimal part is '2'.

Example 1 :

Round 4.834 to the nearest whole number.

Answer :

The first digit after the decimal point in 4.834 is 8, which is greater than 5.

Then, add 1 to the whole number part 4, drop the decimal point and all the digits after it.

So, 4.834 rounded to the nearest whole number is 5.

Example 2 :

Round 7.391 to the nearest whole number.

Answer :

The first digit after the decimal point in 7.391 is 3, which is less than 5.

Then, keep the whole number part 7 as it is, drop the decimal point and all the digits after it.

So, 7.391 rounded to the nearest whole number is 7.

Example 3 :

Round 9.0631 to the nearest whole number.

Answer :

The first digit after the decimal point is 0, which is less than 5.

Then, keep the whole number part 9 as it is, drop the decimal point and all the digits after it.

So, 9.0631 rounded to the nearest whole number is 9.

Example 4 :

Round 0.8105 to the nearest whole number.

Answer :

The first digit after the decimal point in 0.8105 is 8, which is greater than 5.

Then, add 1 to the whole number part 0, drop the decimal point and all the digits after it.

So, 0.8105 rounded to the nearest whole number is 1.

Examples 5-6 : Round each of the following numbers to the nearest whole number :

Example 5 :

Answer :

The first digit after the decimal point in 7.4 is 4, which is less than 5.

Then, keep the whole number part 7 as it is, drop the decimal point and all the digits after it.

Therefore, 7.4 rounded to the nearest whole number is 7.

Example 6 :

Answer :

The first digit after the decimal point in 2.75 is 7, which is greater than 5.

Then, add 1 to the whole number part 2, drop the decimal point and all the digits after it.

Therefore, 2.75 rounded to the nearest whole number is 3.

Example 7 :

In a town, 49.85% of the people living are female. Round this figure to the nearest whole number.

Answer :

The first digit after the decimal point in 49.85 is 8, which is greater than 5.

Then, add 1 to the whole number part 49, drop the decimal point and all the digits after it.

So, 49.85% rounded to the nearest whole number is 50%.

Example 8 :

If the radius of a circle is 9 am, find its circumference. Use the value of π from your calculator and round your answer to the nearest whole number.

Answer :

Formula for circumference of a circle :

= 2πr

Substitute r = 9.

= 2π(9)

= 18π

Using calculator for the value of π,

= 56.548......

The first digit after the decimal point in 56.548...... is 5, which is greater than 5.

Then, add 1 to the whole number part 56, drop the decimal point and all the digits after it.

56.548...... rounded to the nearest whole number is 57.

Therefore, the circumference of the circle is about 57 cm.

Example 9 :

If the radius of a circle is 15 am, find its area. Use the value of π from your calculator and round your answer to the nearest whole number.

Answer :

Formula for area of a circle :

= πr²

Substitute r = 15.

= π(15)²

= 225π

Using calculator for the value of π,

= 706.8583.......

In 706.858......, the first digit after the decimal point is 8, which is greater than 5.

Then, add 1 to the whole number part 706, drop the decimal point and all the digits after it.

706.8583....... rounded to the nearest whole number is 707.

Therefore, the area of the circle is about 707 cm².

Example 10 :

Adam was asked to round 8.7 to the nearest whole number and his answer was 87. Explain Adam's mistake and find the correct answer.

Answer :

Instead of rounding to the nearest whole number, Adam shifted the decimal point to the right by one place.

The correct answer is 9.

Example 11 :

Michael writes down two numbers, W and X. Both W and X have 1 decimal place. Michael rounds W to the nearest whole number and calls his answer Y. He rounds X to the nearest whole number and calls his answer Z. Michael says the difference between W and X cannot be the same as the difference between Y and Z. Show that he is incorrect.

Answer :

Let W = 3.8 and X = 2.8.

The difference between W and X :

= 3.8 - 2.8

= 1

Given : Michael rounds W to the nearest whole number and calls his answer Y. He rounds X to the nearest whole number and calls his answer Z.

Then, Y = 4 and Z = 3.

The difference between Y and Z :

= 4 - 3

= 1

The difference between W and X and the difference between Y and Z are same.

But, Michael says that the difference between W and X cannot be the same as the difference between Y and Z.

So, Michael is incorrect.

Example 12 :

Jessica rounded a number to the nearest whole number and her answer is 23. Write down 10 different possible numbers that she could have rounded.

Answer :

22.5

22.6

22.7

22.8

22.9

23.0

23.1

23.2

23.3

23.4

Practice Questions

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