\begin{tabular}{l} Writing a signed number for a real-world situation \\ Fill in the blanks below. \\ (a) The population of a certain city decreased by 3000 people. \\ Write a signed number to represent this population change. \\ (b) An airport is located 494 feet above sea level. \\ Write a signed number to represent this elevation. \\ Expland \\ \hline\end{tabular}

In the case of the population decrease by 3000 people, the signed number that represents this change would be -3000. This negative sign indicates a reduction in the population, showing that there are 3000 fewer people in the city than before. Signed numbers are essential in illustrating changes in population dynamics, finances, and various other real-world scenarios that involve increases or decreases. For the airport elevation of 494 feet above sea level, the signed number would be +494. The positive sign indicates that the airport is above the reference point of sea level. In similar contexts, elevations above sea level are often represented with positive signs while elevations below (like those in a valley or underwater) would use negative signed numbers, illustrating the concept of relative measurement in geographic positions.