APPENDIX STUDENT'St CRITICAL VALUES This table shows the f-value that defines the area for the stated degrees of freedom (d.f.) Confidence Level Confidence Level 80 .90 95 .98 .99 80 .90 .95 .98 .99 Significance Level for Two-Tailed Test Significance Level for Two-Tailed Test .20 .20 10 05 02 01 10 .02 .01 05 Significance Level for One-Tailed Test Significance Level for One-Tailed Test .005 d.f. 10 05 025 01 d.f. .10 05 025 .01 .005 6.314 1 3.078 12.706 31.821 63.657 36 1.306 1.688 2.028 2.434 2.719 2.920 2.715 2 1.886 4.303 6.965 9.925 37 1.305 1.687 2.026 2.431 1.638 4.541 1.686 2.024 2.353 3.182 5.841 38 1.304 2.429 2.712 2.132 2.776 3.747 2.708 4 1.533 4.604 39 1.304 1.685 2.023 2.426 2.015 2.571 2.021 2.423 2.704 5 1.476 3.365 4.032 40 1.303 1.684 6 1.440 1.943 2.447 3.143 3.707 41 1.303 1.683 2.020 2.421 2.701 2.018 2.418 7 1.415 1.895 2.365 2.998 3.499 42 1.302 1.682 2.698 1.860 2.306 2.695 1.397 2.896 3.355 43 1.302 1.681 2.017 2.416 2.821 3.250 2.015 2.414 9 1.383 1.833 2.262 44 1.301 1.680 2.692 3.169 1.301 2.412 2.690 10 1.372 1.812 2.228 2.764 45 1.679 2.014 2.718 3.106 11 1.363 1.796 2.201 46 1.300 1.679 2.013 2.410 2.687 12 1.356 1.782 2.179 2.681 3.055 47 1.300 1.678 2.012 2.408 2.685 2.407 2.682 13 1.350 1.771 2.160 2.650 3.012 48 1.299 1.677 2.011 2.977 2.010 2.405 2.680 14 1.345 1.761 2.145 2.624 49 1.299 1.677 1.341 2.403 15 1.753 2.131 2.602 2.947 50 1.299 1.676 2.009 2.678 2.668 55 1.297 1.673 2.396 16 1.337 1.746 2.120 2.583 2.921 2.004 17 1.333 1.740 2.110 2.567 2.898 60 1.296 1.671 2.000 2.390 2.660 18 1.330 1.734 2.101 2.552 2.878 65 1.295 1.669 1.997 2.385 2.654 1.328 1.729 19 2.093 2.539 2.861 70 1.294 1.667 1.994 2.381 2.648 2.643 20 1.325 1.725 2.086 2.528 2.845 75 1.293 1.665 1.992 2.377 21 1.323 80 1.292 1.721 2.080 2.518 2.831 1.664 1.990 2.374 2.639 2.819 1.292 2.635 22 1.321 1.717 2.074 2.508 85 1.663 1.988 2.371 1.319 23 1.714 2.069 2.500 2.807 90 1.291 1.662 1.987 2.368 2.632 1.291 1.661 24 1.318 1.711 2.064 2.492 2.797 95 1.985 2.366 2.629 2.626 25 1.316 1.708 2.060 2.485 2.787 100 1.290 1.660 1.984 2.364 1.706 26 1.315 2.056 2.479 2.779 110 1.289 1.659 1.982 2.361 2.621 1.703 2.473 1.658 2.358 27 1.314 2.052 2.771 120 1.289 1.980 2.617 2.614 28 1.313 1.701 2.048 2.467 2.763 130 1.288 1.657 1.978 2.355 2.045 29 1.311 1.699 2.462 2.756 140 1.288 1.656 1.977 2.353 2.611 2.042 1.287 30 1.310 1.697 2.457 2.750 150 1.655 1.976 2.351 2.609 1.696 31 1.309 2.040 2.453 2.744 1.282 1.645 1.960 2.326 2.576 32 1.309 1.694 2.037 2.449 2.738 1.308 2.035 33 1.692 2.445 2.733 2.032 2.441 2.728 34 1.307 1.691 1.306 1.690 35 2.030 2.438 2.724 Note: As n increases, critical values of Student's t approach the z-values in the last line of this table. A common rule of thumb is to usez when n 30, but that is not conservative. 8
A random sample of 11 items is drawn from a population whose standard deviation is unknown. The sample
(a) Construct an
The 98% confidence interval is from ______ to ________
(b) Construct an interval estimate of μ with 98% confidence, assuming that s = 40. (Round your answers to 3 decimal places.)
The 98% confidence interval is from _______ to ________
(c) Construct an interval estimate of μ with 98% confidence, assuming that s = 80. (Round your answers to 3 decimal places.)
The 98% confidence interval is from ______ to ________
(d) Describe how the confidence interval changes as s increases.
-
The interval stays the same as s increases.
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The interval gets wider as s increases.
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The interval gets narrower as s increases.
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