Final answer:
The expression provided indicates a 50% rate of change when considering the square of 0.50, associated with each unit of x in the expression. Therefore, the correct answer is (b) 50%.
Step-by-step explanation:
The expression given is 70 * (1 - 0.50)²x. To determine the percent rate of change, we identify the part of the expression that signifies change, which is (1 - 0.50), or simply 0.50 when expressed as a decimal. In percentage terms, 0.50 is equivalent to a 50% change. However, since it is squared, this indicates the change is exponential or occurring twice in the context of the expression. Therefore, for each unit of x, the initial amount is multiplied by 0.50 twice.
Using the Rule of 70, we can calculate the doubling time of an investment or growth process by dividing 70 by the percentage growth rate. For example, if a variable grows at a rate of 2% per year, it will take 35 years (70/2) to double. In this question, however, the information provided by the Rule of 70 isn't directly applicable since we're not assessing doubling time.
Comparing the options provided, since the expression includes a 50% change, the correct answer would be (b) 50%, because the rest of the percent yields provided, such as 35%, 40%, etc., are not relevant to the immediate calculation required by the given expression.