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Dylan Jones kept careful records of the fuel efficiency of his new car. After the first nine times he filled up the tank, he found the mean was 25.7 miles per gallon (mpg) with a sample standard deviation of 0.9 mpg. (a) Compute the 95 percent confidence interval for his mpg. (Round your answers to 3 decimal places.) I got 25.008 and 26.392 and they are wrong. Professor said "end points of the confidence interval are 20.452 and 22.148 mpg, found by 21.3±2.998(0.8/square root of 8)." Are your using t or z? Since your sample is 9, use t.  Instead of finding z, you have to replace it with t-distribution. I attached the t-distribution chart. to find the correct #, use df=(n-1), which I believe was df=(10-1) = 9. Then correspond with the confidence interval %, which I think was 95%. Can you help.

Dylan Jones kept careful records of the fuel efficiency of his new car. After the first nine times he filled up the tank, he found the mean was 25.7 miles per gallon (mpg) with a sample standard deviation of 0.9 mpg. (a) Compute the 95 percent confidence interval for his mpg. (Round your answers to 3 decimal places.) I got 25.008 and 26.392 and they are wrong. Professor said "end points of the confidence interval are 20.452 and 22.148 mpg, found by 21.3±2.998(0.8/square root of 8)." Are your using t or z? Since your sample is 9, use t.  Instead of finding z, you have to replace it with t-distribution. I attached the t-distribution chart. to find the correct #, use df=(n-1), which I believe was df=(10-1) = 9. Then correspond with the confidence interval %, which I think was 95%. Can you help.

MATLAB: An Introduction with Applications
MATLAB: An Introduction with Applications
6th Edition
ISBN:9781119256830
Author:Amos Gilat
Publisher:Amos Gilat
Chapter1: Starting With Matlab
Section: Chapter Questions
Problem 1P
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Dylan Jones kept careful records of the fuel efficiency of his new car. After the first nine times he filled up the tank, he found the mean was 25.7 miles per gallon (mpg) with a sample standard deviation of 0.9 mpg.

(a) Compute the 95 percent confidence interval for his mpg. (Round your answers to 3 decimal places.)

I got 25.008 and 26.392 and they are wrong. Professor said "end points of the confidence interval are 20.452 and 22.148 mpg, found by 21.3±2.998(0.8/square root of 8)."

Are your using t or z? Since your sample is 9, use t.

 Instead of finding z, you have to replace it with t-distribution. I attached the t-distribution chart. to find the correct #, use df=(n-1), which I believe was df=(10-1) = 9. Then correspond with the confidence interval %, which I think was 95%. Can you help.

-t t -t 0 t 0 t -t o t Confidence interval Left-tailed test Right-tailed test Two-tailed test Confidence Intervals, c Confidence Intervals, c 80% 90% 95% 98% 99% 99.9% 80% 90% 95% 98% 99% 99.9% Level of Significance for One-Tailed Test, a Level of Significance for One-Tailed Test, a df 0.10 0.05 0.025 0.01 0.005 0.0005 df 0.10 0.05 0.025 0.01 0.005 0.0005 Level of Significance for Two-Tailed Test, a Level of Significance for Two-Tailed Test, a 0.20 0.10 0.05 0.02 0.01 0.001 0.20 0.10 0.05 0.02 0.01 0.001 3.078 6.314 12.706 31.821 63.657 9.925 636.619 36 1.306 1.305 1.688 2.028 2.434 2.719 2.715 2.712 2.708 2.704 3.582 3.574 1.886 1.638 1.533 1.476 2.920 2.353 2.132 4.303 3.182 2.776 6.965 4.541 31.599 37 1.687 2.026 2.431 5.841 12.924 8.610 6.869 38 1.304 1.686 2.024 2.023 2.429 2.426 3.566 3.747 3.365 4.604 1.304 1.303 39 1.685 3.558 2.015 2.571 4.032 40 1.684 2.021 2.423 3.551 2.447 2.365 1.943 3.143 1.303 1.683 2.020 2.018 2.017 2.701 2.698 2.695 1.440 3.544 3.707 3.499 3.355 5.959 41 2.421 7 1.415 1.895 1.860 1.833 1.812 2.998 2.896 5.408 42 1.302 1.302 1.682 1.681 2.418 2.416 3.538 3.532 8 1.397 2.306 5.041 43 9 1.383 2.262 2.821 3.250 4.781 44 1.301 1.680 2.015 2.414 2.692 2.690 3.526 10 1.372 2.228 2.764 3.169 4.587 45 1.301 1.679 2.014 2.412 3.520 1.363 1.356 1.350 1.345 11 1.796 1.782 1.771 1.761 1.753 2.201 2.718 3.106 3.055 4.437 46 1.300 1.679 2.013 2.410 2.687 2.685 2.682 2.680 2.678 3.515 12 2.179 2.681 4.318 47 1.300 1.678 2.012 2.408 3.510 3.505 3.500 13 2.160 2.145 2.650 2.624 3.012 4.221 48 1.299 1.299 1.299 1.677 1.677 1.676 2.011 2.407 2.405 2.403 14 2.977 4.140 49 2.010 15 1.341 2.131 2.602 2.947 4.073 50 2.009 3.496 1.337 1.333 1.330 1.328 1.325 1.746 1.740 2.583 2.567 2.552 2.539 2.528 1.298 1.298 1.298 1.297 1.297 1.675 1.675 1.674 1.674 1.673 2.402 2.400 2.676 2.674 3.492 3.488 2.120 2.110 2.101 2.093 2.086 2.008 2.007 16 2.921 2.898 2.878 2.861 2.845 4.015 51 17 3.965 52 18 1.734 1.729 1.725 3.922 53 2.006 2.005 2.004 2.399 2.672 2.670 2.668 3.484 19 3.883 3.850 54 2.397 3.480 20 55 2.396 3.476 2.003 2.002 21 1.323 1.721 2.080 2.074 2.518 2.831 2.819 2.807 2.797 2.787 3.819 56 1.297 2.508 2.500 1.673 1.672 1.672 2.395 2.394 2.667 2.665 3.473 3.470 3.466 22 1.321 1.717 3.792 57 1.297 2.069 2.002 2.001 2.000 23 2.663 1.319 1.318 1.316 1.714 1.711 1.708 3.768 58 1.296 2.392 24 2.064 2.492 2.485 3.745 59 1.296 1.671 1.671 2.391 2.662 2.660 3.463 25 2.060 3.725 60 1.296 2.390 3.460 1.706 1.703 26 1.315 2.056 2.479 2.779 3.707 61 1.296 1.670 2.000 1.999 2.389 2.659 2.657 2.656 3.457 27 2.052 2.048 1.295 1.295 1.295 1.295 1.314 1.313 2.473 2.467 2.462 2.457 2.771 3.690 62 1.670 2.388 2.387 2.386 2.385 3.454 1.669 1.669 1.669 28 1.701 2.763 3.674 63 1.998 3.452 1.699 1.697 1.998 1.997 29 1.311 2.045 2.042 2.756 2.750 3.659 3.646 64 2.655 2.654 3.449 3.447 30 1.310 65 31 1.309 1.696 1.694 1.692 2.040 2.037 2.035 2.032 2.030 2.453 2.449 2.445 2.744 3.633 66 1.295 1.668 1.997 1.996 1.995 1.995 1.994 2.384 2.652 3.444 32 1.309 1.308 2.738 3.622 3.611 67 1.294 1.668 2.383 2.651 3.442 33 2.733 68 1.294 1.668 2.382 2.650 3.439 2.649 2.648 34 1.294 1.307 1.306 1.691 2.441 2.728 3.601 69 1.667 1.667 2.382 2.381 3.437 35 1.690 2.438 2.724 3.591 70 1.294 3.435 3.403 3.402 71 1.294 1.667 1.994 2.380 2.647 3.433 89 1.291 1.662 1.662 1.987 2.369 2.368 2.632 2.632 2.646 2.645 2.644 2.643 1.993 1.993 72 1.293 1.666 1.666 1.666 1.665 2.379 3.431 90 1.291 1.987 3.429 3.427 73 1.293 2.379 1.986 1.986 1.986 1.986 1.985 91 1.291 1.291 1.662 1.662 2.368 2.368 2.367 2.367 2.366 2.631 2.630 2.630 3.401 3.399 3.398 3.397 3.396 1.293 2.378 2.377 74 1.993 1.992 75 1.293 3.425 92 93 1.291 1.661 1.992 1.991 1.991 1.990 1.990 76 1.293 1.665 2.376 2.642 3.423 94 1.291 1.661 2.629 77 1.293 1.665 1.665 1.664 1.664 2.376 2.375 2.374 2.374 2.641 3.421 95 1.291 1.661 2.629 2.640 2.640 2.639 78 1.292 1.292 1.292 3.420 96 3.395 1.290 1.290 1.290 1.290 1.661 1.661 1.661 1.660 1.985 1.985 1.984 1.984 2.366 2.365 2.365 2.365 2.364 2.628 2.627 2.627 2.626 2.626 79 3.418 3.416 97 3.394 3.393 3.392 3.390 80 98 1.990 1.989 1.989 1.989 1.988 2.638 2.637 2.636 2.636 2.635 81 1.292 1.292 1.664 1.664 1.663 1.663 2.373 3.415 99 82 2.373 3.413 100 1.290 1.660 1.984 83 1.292 2.372 2.372 3.412 120 3.373 1.289 1.288 1.287 1.286 1.286 1.282 1.658 1.656 1.980 1.977 1.975 1.973 1.972 1.960 2.358 2.617 2.611 2.607 2.603 84 1.292 3.410 140 2.353 2.350 2.347 85 1.292 1.663 2.371 3.409 3.361 160 1.654 1.653 1.653 1.645 3.352 1.663 1.663 1.662 86 1.291 1.988 2.370 2.634 3.407 180 3.345 87 1.291 1.988 1.987 2.370 2.634 3.406 200 2.345 2.326 2.601 3.340 3.291 88 1.291 2.369 2.633 3.405 2.576 00 2345
Transcribed Image Text:-t t -t 0 t 0 t -t o t Confidence interval Left-tailed test Right-tailed test Two-tailed test Confidence Intervals, c Confidence Intervals, c 80% 90% 95% 98% 99% 99.9% 80% 90% 95% 98% 99% 99.9% Level of Significance for One-Tailed Test, a Level of Significance for One-Tailed Test, a df 0.10 0.05 0.025 0.01 0.005 0.0005 df 0.10 0.05 0.025 0.01 0.005 0.0005 Level of Significance for Two-Tailed Test, a Level of Significance for Two-Tailed Test, a 0.20 0.10 0.05 0.02 0.01 0.001 0.20 0.10 0.05 0.02 0.01 0.001 3.078 6.314 12.706 31.821 63.657 9.925 636.619 36 1.306 1.305 1.688 2.028 2.434 2.719 2.715 2.712 2.708 2.704 3.582 3.574 1.886 1.638 1.533 1.476 2.920 2.353 2.132 4.303 3.182 2.776 6.965 4.541 31.599 37 1.687 2.026 2.431 5.841 12.924 8.610 6.869 38 1.304 1.686 2.024 2.023 2.429 2.426 3.566 3.747 3.365 4.604 1.304 1.303 39 1.685 3.558 2.015 2.571 4.032 40 1.684 2.021 2.423 3.551 2.447 2.365 1.943 3.143 1.303 1.683 2.020 2.018 2.017 2.701 2.698 2.695 1.440 3.544 3.707 3.499 3.355 5.959 41 2.421 7 1.415 1.895 1.860 1.833 1.812 2.998 2.896 5.408 42 1.302 1.302 1.682 1.681 2.418 2.416 3.538 3.532 8 1.397 2.306 5.041 43 9 1.383 2.262 2.821 3.250 4.781 44 1.301 1.680 2.015 2.414 2.692 2.690 3.526 10 1.372 2.228 2.764 3.169 4.587 45 1.301 1.679 2.014 2.412 3.520 1.363 1.356 1.350 1.345 11 1.796 1.782 1.771 1.761 1.753 2.201 2.718 3.106 3.055 4.437 46 1.300 1.679 2.013 2.410 2.687 2.685 2.682 2.680 2.678 3.515 12 2.179 2.681 4.318 47 1.300 1.678 2.012 2.408 3.510 3.505 3.500 13 2.160 2.145 2.650 2.624 3.012 4.221 48 1.299 1.299 1.299 1.677 1.677 1.676 2.011 2.407 2.405 2.403 14 2.977 4.140 49 2.010 15 1.341 2.131 2.602 2.947 4.073 50 2.009 3.496 1.337 1.333 1.330 1.328 1.325 1.746 1.740 2.583 2.567 2.552 2.539 2.528 1.298 1.298 1.298 1.297 1.297 1.675 1.675 1.674 1.674 1.673 2.402 2.400 2.676 2.674 3.492 3.488 2.120 2.110 2.101 2.093 2.086 2.008 2.007 16 2.921 2.898 2.878 2.861 2.845 4.015 51 17 3.965 52 18 1.734 1.729 1.725 3.922 53 2.006 2.005 2.004 2.399 2.672 2.670 2.668 3.484 19 3.883 3.850 54 2.397 3.480 20 55 2.396 3.476 2.003 2.002 21 1.323 1.721 2.080 2.074 2.518 2.831 2.819 2.807 2.797 2.787 3.819 56 1.297 2.508 2.500 1.673 1.672 1.672 2.395 2.394 2.667 2.665 3.473 3.470 3.466 22 1.321 1.717 3.792 57 1.297 2.069 2.002 2.001 2.000 23 2.663 1.319 1.318 1.316 1.714 1.711 1.708 3.768 58 1.296 2.392 24 2.064 2.492 2.485 3.745 59 1.296 1.671 1.671 2.391 2.662 2.660 3.463 25 2.060 3.725 60 1.296 2.390 3.460 1.706 1.703 26 1.315 2.056 2.479 2.779 3.707 61 1.296 1.670 2.000 1.999 2.389 2.659 2.657 2.656 3.457 27 2.052 2.048 1.295 1.295 1.295 1.295 1.314 1.313 2.473 2.467 2.462 2.457 2.771 3.690 62 1.670 2.388 2.387 2.386 2.385 3.454 1.669 1.669 1.669 28 1.701 2.763 3.674 63 1.998 3.452 1.699 1.697 1.998 1.997 29 1.311 2.045 2.042 2.756 2.750 3.659 3.646 64 2.655 2.654 3.449 3.447 30 1.310 65 31 1.309 1.696 1.694 1.692 2.040 2.037 2.035 2.032 2.030 2.453 2.449 2.445 2.744 3.633 66 1.295 1.668 1.997 1.996 1.995 1.995 1.994 2.384 2.652 3.444 32 1.309 1.308 2.738 3.622 3.611 67 1.294 1.668 2.383 2.651 3.442 33 2.733 68 1.294 1.668 2.382 2.650 3.439 2.649 2.648 34 1.294 1.307 1.306 1.691 2.441 2.728 3.601 69 1.667 1.667 2.382 2.381 3.437 35 1.690 2.438 2.724 3.591 70 1.294 3.435 3.403 3.402 71 1.294 1.667 1.994 2.380 2.647 3.433 89 1.291 1.662 1.662 1.987 2.369 2.368 2.632 2.632 2.646 2.645 2.644 2.643 1.993 1.993 72 1.293 1.666 1.666 1.666 1.665 2.379 3.431 90 1.291 1.987 3.429 3.427 73 1.293 2.379 1.986 1.986 1.986 1.986 1.985 91 1.291 1.291 1.662 1.662 2.368 2.368 2.367 2.367 2.366 2.631 2.630 2.630 3.401 3.399 3.398 3.397 3.396 1.293 2.378 2.377 74 1.993 1.992 75 1.293 3.425 92 93 1.291 1.661 1.992 1.991 1.991 1.990 1.990 76 1.293 1.665 2.376 2.642 3.423 94 1.291 1.661 2.629 77 1.293 1.665 1.665 1.664 1.664 2.376 2.375 2.374 2.374 2.641 3.421 95 1.291 1.661 2.629 2.640 2.640 2.639 78 1.292 1.292 1.292 3.420 96 3.395 1.290 1.290 1.290 1.290 1.661 1.661 1.661 1.660 1.985 1.985 1.984 1.984 2.366 2.365 2.365 2.365 2.364 2.628 2.627 2.627 2.626 2.626 79 3.418 3.416 97 3.394 3.393 3.392 3.390 80 98 1.990 1.989 1.989 1.989 1.988 2.638 2.637 2.636 2.636 2.635 81 1.292 1.292 1.664 1.664 1.663 1.663 2.373 3.415 99 82 2.373 3.413 100 1.290 1.660 1.984 83 1.292 2.372 2.372 3.412 120 3.373 1.289 1.288 1.287 1.286 1.286 1.282 1.658 1.656 1.980 1.977 1.975 1.973 1.972 1.960 2.358 2.617 2.611 2.607 2.603 84 1.292 3.410 140 2.353 2.350 2.347 85 1.292 1.663 2.371 3.409 3.361 160 1.654 1.653 1.653 1.645 3.352 1.663 1.663 1.662 86 1.291 1.988 2.370 2.634 3.407 180 3.345 87 1.291 1.988 1.987 2.370 2.634 3.406 200 2.345 2.326 2.601 3.340 3.291 88 1.291 2.369 2.633 3.405 2.576 00 2345
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