Question

reinforce mary is doing research on bird migration. last week she counted 12 migratory birds in her yard. this week she counted 10. what was the percent decrease in birds this week?

Explanation:

Step1: Calculate the difference in the number of birds

The formula for the difference is \( \text{Difference}=\text{Last week's count}-\text{This week's count} \).
Given that last week's count is \( 12 \) and this week's count is \( 10 \), so \( \text{Difference}=12 - 10=2 \).

Step2: Calculate the percentage decrease

The formula for percentage decrease is \( \text{Percentage decrease}=\frac{\text{Difference}}{\text{Original amount}}\times100\% \).
The original amount is the number of birds last week (\( 12 \)). So \( \text{Percentage decrease}=\frac{2}{12}\times 100\%=\frac{1}{6}\times100\%\approx 16.67\% \).

Answer:

The percent decrease in birds this week is approximately \( 16.67\% \)