Using a quadratic regression equation, it is found that the prediction of volunteers in year 10 is of:
A. 47.
<h3>How to find the equation of quadratic regression using a calculator?</h3>
To find the equation, we need to insert the points (x,y) in the calculator.
In this problem, we have that the function initially increases, then it decreases, which means that it is a quadratic function. The points (x,y) to be inserted into the calculator are given as follows:
(1, 20), (2,17), (3, 16), (4,16), (5,18), (6,21), (7,25), (8,31)
Inserting these points into the calculator, the prediction of y for a value of x is given as follows:
y = 0.702x^2 - 4.726x + 23.857
Hence, when x = 10, the prediction is:
y = 0.702 x 10² - 4.726 x 10 + 23.857
y = 47.
Hence option A is correct.
More can be learned about a quadratic regression equation at brainly.com/question/24028025
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. This is because when plugging in -2 for x, the expression will look like this: 
. To make the exponent positive, you have to flip it into a fraction. Then it will be 
. Lastly, you simplify the denominator into 81.
