In 2015 the populations of City X and City Y were equal. From 2010 to 2015, the population of City X increased by 20% and the population of City Y decreased by 10%. If the population of City X was 120,000 in 2010, what was the population of City Y in 2010?

Explanation

To solve the problem, start with City X. It had a population of 120,000 in 2010, and with a 20% increase, its population in 2015 was 120,000 × 1.20 = 144,000. For City Y, let y represent the population in 2010. A 10% decrease means the 2015 population is y × 0.90. Since both populations are equal in 2015: y × 0.90 = 144,000. Solving this gives y = 144,000 / 0.90 = 160,000. Thus, City Y's population in 2010 was 160,000. The other options do not match this outcome when recalculated with the given percentage changes.