Answer
There is a 90% confidence that the mean percent infected is between 3.43 and 4.73
The beetle is helpful in controlling the weed
Work Step by Step
+- = plus minus
$x +- t x \frac{8}{\sqrt n} = 4.08 +- 1.70 x 2.01/\sqrt 28 = 4.08 \pm .65$
This means there is a 90% confidence that the mean percent infected is between 3.43 and 4.73.
