29. Copper production increased at a rate of about \( 4.9 \% \) per year between 1988 and 1993 . In 1993 , copper production was approximately 1.801 billion kilograms. If this trend continued, which is the best model of copper production (P), in billions of kg , since 1993 ? \( \begin{array}{ll}\text { a) } p=1.801(4.900)^{t} & \text { b) } p=1.801(1.490)^{t} \\ \begin{array}{ll}\text { c) } p=1.801(1.049)^{t} & \text { d) } p=1.801(0.049)^{t}\end{array}\end{array} \begin{array}{l}\text { A }\end{array} \)

To model copper production after 1993, you need to account for the annual growth rate of 4.9%. When we express growth as a factor, we add 1 to the growth rate in decimal form. Hence, a 4.9% increase translates to multiplying by 1.049 every year. Therefore, the best model for copper production (P) is given by the expression in option c: \( p=1.801(1.049)^{t} \). One common mistake when working with percentage growth is to confuse the base growth factor with the percentage itself. Remember, when we say a quantity increases by 4.9%, you’re actually using the factor \( 1.049 \), not \( 4.900 \) or \( 0.049 \). Keeping this distinction clear will save you from making calculation errors in models involving growth!