Sometimes we just need a rough or round answer to a question. When we are faced with a long number, we could round it off to the nearest hundred, or nearest thousand. And when we get a long decimal answer, we could round it off to a certain number of decimal places.
Another method of giving an approximated answer is to round off using significant figures.
The word significant means important. The closer a digit is to the beginning of a number, the more significant it is.
Example 1:
With the number 4657, the 4 is the most significant digit, because it tells us that the number is 4 thousand and something. It follows that the 6 is the next most significant, and so on.
Example 2:
With the number 0.0000076253, the 7 is the most significant digit, because it tells us that the number is 7 millionths and something. The 6 is the next most significant, and so on.
We round off a number using a certain number of significant figures. The most common are 1, 2 or 3 significant figures.
Remember the rules for rounding up:
If the next number is 5 or more, you round up.
If the next number is 4 or less, you do not round up.
Question 1:
Round £43884 to 2 sig. figs. (significant figures).
Question 2:
What is 0.023478 to 3 sig. figs.?
Question 3:
Round 3333 to 2 sig. figs.
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Answers:
1.) £44000
2.) 0.0235
3.) 3300
