Rounding can be useful when dealing with large or complicated numbers, or when we only need an approximate answer. In this lesson, we will learn about the different methods of rounding and how to use them.
Method of Rounding
There are several methods of rounding, but the two most common are rounding to a certain number of decimal places and rounding to a certain number of significant figures.
Rounding to a certain number of decimal places:
When rounding to a certain number of decimal places, we look at the digit to the right of the desired decimal place. If that digit is 5 or greater, we round up the previous digit; otherwise, we round down the previous digit.
For example, if we want to round 3.14159 to 2 decimal places, we look at the third decimal place, which is 1. Since 1 is less than 5, we round down the previous digit, which is 4, and get 3.14.
Rounding to a certain number of significant figures:
When rounding to a certain number of significant figures, we look at the first non-zero digit from the left. We then count the total number of digits, including the first non-zero digit. If the next digit is 5 or greater, we round up the last digit; otherwise, we leave it unchanged.
For example, if we want to round 123.45 to 3 significant figures, we look at the first non-zero digit, which is 1. We count the total number of digits, which is 5. Since the next digit, 4, is less than 5, we leave the last digit, 5, unchanged and get 123.
Practice Exercise
Now let’s try some practice exercises to reinforce the concept of rounding:
- Round 4.678 to 2 decimal places.
Answer: 4.68
- Round 456.789 to 3 significant figures.
Answer: 457
- Round 0.000045678 to 4 significant figures.
Answer: 0.000046
- Round 987.654 to 1 decimal place.
Answer: 987.7
Rounding is an essential skill in mathematics that allows us to estimate and approximate numbers to a certain degree of accuracy. By using the two most common methods of rounding, rounding to a certain number of decimal places and rounding to a certain number of significant figures, we can make our calculations more manageable and meaningful.