Statistics question, please help me understand

Question

Assuming the 95% confidence interval of your group difference is [-5,15], which of the following would be a plausible 90% confidence interval?

1. [-8,18]
2. [8,20]
3. [-2,12]
4. [-5,3]

Answer 1

A 90% confidence interval will be centered about the same point estimate (5) as the 95% confidence interval, however, it will have a smaller margin of error (less width), so the correct answer is [-2,12].