S E = tcn Level of confidence, c 0.80 0.90 0.95 0.98 0.99 One tall, a 0.10 0.05 0.025 0.01 0.005 d.f. Two tails, a 0.20 0.10 0.05 0.02 0.01 1 2 3 3.078 6.314 1.886 2.920 1.638 2.353 1.533 2.132 12.706 31.821 63.657 5 1.476 2.015 2.571 4.303 6.965 9.925 3.182 4.541 5.841 2.776 3.747 4.604 3.365 4.032 c-confidence interval 6 1.440 1.943 2.447 3.143 3.707 7 1.415 1.895 2.365 2.998 3.499 8 1.397 1.860 2.306 2.896 3.355 9 1.383 1.833 2.262 2.821 3.250 10 1.372 1.812 2.228 2.764 3.169 11 1.363 1.796 2.201 2.718 3.106 12 1.356 1.782 2.179 2.681 3.055 Left-tailed test 13 1.350 1.771 2.160 2.650 3.012 14 1.345 1.761 2.145 2.624 2.977 15 1.341 1.753 2.131 2.602 2.947 16 1.337 1.746 2.120 2.583 2.921 17 1.333 1.740 2.110 2.567 2.898 18 1.330 1.734 2.101 2.552 2.878 19 1.328 1.729 2.093 2.539 2.861 20 1.325 1.725 2.086 21 1.323 1.721 2.080 22 1.321 1.717 2.074 2.518 2.508 2.819 2.528 2.845 2.831 Right-tailed test 23 1.319 1.714 2.069 2.500 2.807 24 1.318 1.711 2.064 2.492 2.797 25 1.316 1.708 2.060 26 1.315 1.706 2.485 2.787 2.056 2.479 2.779 a 27 1.314 1.703 2.052 28 1.313 1.701 2.048 2.473 2.771 2.467 2.763 29 1.311 1.699 2.045 2.462 2.756 Two-tailed test 30 1.310 1.697 2.042 2.457 2.750 8. Body Mass Index In a random sample of 50 people, the mean body mass index (BMI) was 27.7 and the standard deviation was 6.12. Assume the body mass indexes are normally distributed. (Adapted from Centers for Disease Control) 9. 10. Mortgages In a random sample of 15 mortgage institutions, the mean interest rate was 4.99% and the standard deviation was 0.36%. Assume the interest rates are normally distributed. (Adapted from Federal Reserve) Hospital Waiting Times In a random sample of 19 patients at a hospital's minor emergency department, the mean waiting time before seeing a medical professional was 23 minutes and the standard deviation was 11 minutes. Assume the waiting times are not normally distributed.