Final answer:
For addition and subtraction, round the result to the least number of decimal places from the original numbers involved. The correct option is a) Round to the same number of decimal places as the number with the least decimal places. For multiplication and division, round to the least number of significant figures from the original numbers involved.
Step-by-step explanation:
The rule for significant figures in addition and subtraction requires that the result be rounded to the same number of decimal places as the number with the least number of decimal places among those being calculated, which is also known as the least certain value. For example, when we add 1.0023 g and 4.383 g, the result should have three decimal places because 4.383 g has three decimal places, which is the smaller number of decimal places compared to 1.0023 g.
Similarly, when we subtract 421.23 g from 486 g, we round the result to two decimal places, since the minuend, 486 g, has no decimal places, and the subtrahend; 421.23 g has two. Therefore, the result keeps two decimal places to match the subtrahend.
Option a accurately describes this rule, stating that one should "Round to the same number of decimal places as the number with the least decimal places." Therefore, answer a) is the correct option for the rule concerning significant figures in addition and subtraction.
For multiplication and division, the rule differs; the result should match the number of significant figures in the number with the least significant figures among the numbers involved in the calculation. For instance, when multiplying 0.6238 cm by 6.6 cm, the product should have two significant figures, as 6.6 cm has two significant figures, which is the smaller number among the two values.