A researcher compares the effectiveness of two different instructional methods for teaching physiology. A sample of 205 students using Method 1 produces a testing average of 81.3. A sample of 194 students using Method 2 produces a testing average of 86.9. Assume that the population standard deviation for Method 1 is 19.89, while the population standard deviation for Method 2 is 19.87. Determine the 90% confidence interval for the true difference between testing averages for students using Method 1 and students using Method 2. Step 1 of 3: Find the point estimate for the true difference between the population means.