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Three years ago, the population of a certain species of bird was calculated at 20 birds per acre. This year, a biologist recorded a total of 47 birds in an area equal to 3.25 acres. By about what percentage has the bird population in the biologist’s sample decreased over the last 3 years, to the nearest tenth?
  • a)
    14.7%
  • b)
    27.7%
  • c)
    38.3%
  • d)
    42.6%
  • e)
    72.3%
Correct answer is option 'B'. Can you explain this answer?
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Verified Answer
Three years ago, the population of a certain species of bird was calcu...
The correct answer is B. This question asks you to calculate the percentage by which the population has decreased. First, determine the number of birds that you would expect to find in your sample area if the population density had not changed. Multiply the population density 3 years ago (20 birds) by the size of the sample area (3.25 acres):
20 × 3.25 = 65
You would expect to find 65 birds in your sample area if there had been no change in population density.
Next, subtract the actual number of birds recorded in the sample area (47) from the expected number of birds (65):
65 − 47 = 18
There are 18 fewer birds in the sample area than what you would expect to find. Since you are asked to calculate the percentage decrease, set up a proportion: 18 birds is to 65 birds as x percent is to 100 percent.
18/65 = x/100
Cross-multiply and solve for x:
65x = 1,800
x = 1,800/65
x = 27.69
Since the problem asks for an answer to the nearest tenth, round to 27.7. According to the study, the population density of the particular bird that you are studying has decreased by approximately 27.7%.
Answer choice C could be obtained if you found the difference between the number of birds expected (65) and the number of birds recorded (47), then divided by the number of birds recorded (47) to get a percent. Answer choice D is the percentage that the number of birds per acre 3 years ago (20) is of the number of birds recorded in 3.5 acres this year (47).
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Most Upvoted Answer
Three years ago, the population of a certain species of bird was calcu...
To find the percentage increase in the bird population, we need to compare the current population to the population three years ago.

The population three years ago was 20 birds per acre. So, the total bird population three years ago would be 20 birds/acre * 3.25 acres = 65 birds.

The percentage increase in the bird population is (47 birds - 65 birds) / 65 birds * 100 = -18/65 * 100 ≈ -27.7%.

Therefore, the bird population has decreased by about 27.7%.
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Three years ago, the population of a certain species of bird was calculated at 20 birds per acre. This year, a biologist recorded a total of 47 birds in an area equal to 3.25 acres. By about what percentage has the bird population in the biologist’s sample decreased over the last 3 years, to the nearest tenth?a)14.7%b)27.7%c)38.3%d)42.6%e)72.3%Correct answer is option 'B'. Can you explain this answer?
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Three years ago, the population of a certain species of bird was calculated at 20 birds per acre. This year, a biologist recorded a total of 47 birds in an area equal to 3.25 acres. By about what percentage has the bird population in the biologist’s sample decreased over the last 3 years, to the nearest tenth?a)14.7%b)27.7%c)38.3%d)42.6%e)72.3%Correct answer is option 'B'. Can you explain this answer? for ACT 2025 is part of ACT preparation. The Question and answers have been prepared according to the ACT exam syllabus. Information about Three years ago, the population of a certain species of bird was calculated at 20 birds per acre. This year, a biologist recorded a total of 47 birds in an area equal to 3.25 acres. By about what percentage has the bird population in the biologist’s sample decreased over the last 3 years, to the nearest tenth?a)14.7%b)27.7%c)38.3%d)42.6%e)72.3%Correct answer is option 'B'. Can you explain this answer? covers all topics & solutions for ACT 2025 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for Three years ago, the population of a certain species of bird was calculated at 20 birds per acre. This year, a biologist recorded a total of 47 birds in an area equal to 3.25 acres. By about what percentage has the bird population in the biologist’s sample decreased over the last 3 years, to the nearest tenth?a)14.7%b)27.7%c)38.3%d)42.6%e)72.3%Correct answer is option 'B'. Can you explain this answer?.
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