Understanding significant figures is essential for accurately conveying the precision of numerical values in scientific contexts. Significant figures are the digits in a number that contribute to its accuracy, and there are straightforward rules to determine how many significant figures a number contains.

The first rule applies when a number includes a decimal point. In this case, you count from left to right, starting with the first non-zero digit and continuing to the end of the number. For example, in the number 0.00252, you would start counting at the first non-zero digit, which is 2, resulting in three significant figures (2, 5, and 2).

The second rule is for numbers without a decimal point. Here, you count from right to left, again starting with the first non-zero digit. For instance, in the number 5004, you would count from the 5 to the end, yielding four significant figures (5, 0, 0, and 4).

The third rule pertains to exact numbers, which are values known with complete certainty, such as counts of objects. Exact numbers have an infinite number of significant figures. For example, if there are 125 students in a class, this number is exact and can be counted, thus it has infinite significant figures. Similarly, a dozen eggs equals 12 eggs, which is also an exact count.

In summary, the first two rules help you determine significant figures based on the presence or absence of a decimal point, while the third rule highlights that exact numbers possess infinite significant figures. Mastering these rules is crucial for ensuring precision in scientific measurements and calculations.