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Calculate Percent Change Problem: The population of a particular city increased from 400,000 to 500,000. Determine the percent change in the population. Key Concept: When determining the percentage of change, compare the amount of the change to the original quantity. For this problem, the amount of change was 100,000 people. The original population was 400,000. To determine the percent change , divide the amount of change by the original quantity. So we say: 100000 400000 .25 Remember, when changing from a decimal to a percent, we move the decimal two places to the right. So: . 𝟐𝟓 = 𝟐𝟓% The population changed by 25%. Just for thought:: If the population had changed from 500,000 to 400,000, we would have divided the amount of the change (100,000) by the original population (500,000) and determined that the population decreased by 20%