CFA Practice Question

There are 434 practice questions for this study session.

CFA Practice Question

To estimate the average weight of the red-crowned woodpecker to within 2 grams at a 95% confidence level, researchers must randomly sample how many red-crowned woodpeckers? (The population can be assumed normal with a standard deviation of 13 grams.)
A. 282
B. 70
C. 163
Explanation: We work with the formula for E, solving it for n, the sample size. First, for a 95% level of confidence, we need z(0.025). Going to the normal table, we get z(0.025) = 1.96. Now, working with the E formula, we get n = 162.3076. So, the sample size needed is n = 163 (if there is a decimal part, we always go to the next whole number).

User Contributed Comments 7

User Comment
haarlemmer IN FACT, IT IS WRONG. WITHIN 2 PERCENT MEANS E=1 NOT 2.
tony1973 haarlemmer: within 2 grams at a 95% level, not 2%.
danlan It means: 2 gram is the critical point for 95% confidence level (related to 1.96 as reliability factor)
Janey I found this easier with trial and error using the equation - 1.96(.3/SQRTn) where n is either A,B,C or D
niko7 haarlemmer, apparently "within 2 grams" assumes on both sides.
Vadik within. I really thought in the range of 2 grams. E=1
birdperson second that vadik
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