To calculate the difference between the average annual trend of water rising and the observed fall in water levels for the specific part of the river Ericka observed, she would follow these steps:
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Calculate the Total Expected Rise: Ericka first needs to determine how much water levels would have risen on average over the 6.2-year period. She can calculate this by multiplying the average annual rise (1.8 mm/year) by the number of years (6.2 years): \[ \text{Total Expected Rise} = \text{Average Annual Rise} \times \text{Time Period} \] \[ \text{Total Expected Rise} = 1.8 \text{ mm/year} \times 6.2 \text{ years} = 11.16 \text{ mm} \]
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Determine the Actual Change in Water Levels: Next, Ericka needs to quantify how much the water level actually fell in the part of the river she observed. This would be a negative value when comparing to the expected rise. For example, if she observed that the water level fell by, say, 3 mm over the same period, this value would be used in her calculations.
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Calculate the Difference: To find the difference between the expected rise and the actual fall, she would subtract the actual change from the total expected rise. It can be represented as: \[ \text{Difference} = \text{Total Expected Rise} - \text{Actual Fall} \] Using the example of a 3 mm fall: \[ \text{Difference} = 11.16 \text{ mm} - (-3 \text{ mm}) = 11.16 \text{ mm} + 3 \text{ mm} = 14.16 \text{ mm} \]
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Interpret the Result: The resulting value shows how much more the water levels were expected to rise compared to what actually happened in the observed area. If the result is positive, it indicates a discrepancy where the actual water levels fell instead of rising as expected.
By following these steps, Ericka would be able to quantify the difference in a clear manner, providing insight into the local changes in water levels compared to the broader trend.
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