A researcher compares the effectiveness of two different instructional methods for teaching pharmacology. A sample of 25

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A researcher compares the effectiveness of two different
instructional methods for teaching pharmacology. A sample
of 257 students using Method 1 produces a testing average
of 50.4. A sample of 280 students using Method 2
produces a testing average of 71.4. Assume the standard
deviation is known to be 8.97 for Method 1
and 17.74 for Method 2. Determine
the 98% confidence interval for the true difference
between testing averages for students using Method 1 and
students using Method 2.
Step 1 of 2:
Find the critical value that should be used in constructing the
confidence interval.