If a river's pollution level decreases from 80 ppm to 20 ppm over 4 years, what

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Question: If a river\'s pollution level decreases from 80 ppm to 20 ppm over 4 years, what is the average annual decrease in pollution level?

Options:

Correct Answer: 15 ppm

Solution:

Average annual decrease = (Initial level - Final level) / Number of years = (80 - 20) / 4 = 60 / 4 = 15 ppm.

If a river's pollution level decreases from 80 ppm to 20 ppm over 4 years, what is the average annual decrease in pollution level?

If a river's pollution level decreases from 80 ppm to 20 ppm over 4 years, what is the average annual decrease in pollution level?

Step 1: Identify the initial pollution level, which is 80 ppm.
Step 2: Identify the final pollution level, which is 20 ppm.
Step 3: Calculate the total decrease in pollution level by subtracting the final level from the initial level: 80 ppm - 20 ppm.
Step 4: Perform the subtraction: 80 - 20 = 60 ppm.
Step 5: Identify the number of years over which this decrease occurred, which is 4 years.
Step 6: Calculate the average annual decrease by dividing the total decrease by the number of years: 60 ppm / 4 years.
Step 7: Perform the division: 60 / 4 = 15 ppm.

Average Rate of Change – This concept involves calculating the average change in a quantity over a specified period, which in this case is the pollution level of a river over 4 years.
Unit Conversion – Understanding that the result is expressed in parts per million (ppm) and ensuring the units remain consistent throughout the calculation.