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P1

En Navarra, aproximadamente un 1,4 %1{,}4\,\% de la población es intolerante al gluten. Un test de intolerancia al gluten tiene una sensibilidad del 97 %97\,\% (es decir, si se aplicase a 100 personas intolerantes al gluten, se espera que 97 darían positivo y 3 negativo). El mismo test tiene una especificidad del 96 %96\,\% (aplicando el test a 100 personas sin intolerancia, 96 darían negativo y 4 positivo). Elegimos una persona al azar:
i
¿Cuál es la probabilidad de que el test le dé positivo?
ii
¿Cuál es la probabilidad de que le dé negativo?
iii
¿Cuál es la probabilidad de que, si le da positivo el test, sea intolerante al gluten?

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AYUDA Volumen de una esfera: 43πR3\frac{4}{3}\pi R^3 Área de una esfera: 4πR24\pi R^2 Ecuación de circunferencia de radio RR centrada en (a,b)(a, b): (x−a)2+(y−b)2=R2(x - a)^2 + (y - b)^2 = R^2 Z∼N(0,1)Z \sim N(0, 1)
kk0123456789
−3,50,00020,00020,00020,00020,00020,00020,00020,00020,00020,0002
−3,40,00030,00030,00030,00030,00030,00030,00030,00030,00030,0002
−3,30,00050,00050,00050,00040,00040,00040,00040,00040,00040,0003
−3,20,00070,00070,00060,00060,00060,00060,00060,00050,00050,0005
−3,10,00100,00090,00090,00090,00080,00080,00080,00080,00070,0007
−3,00,00130,00130,00130,00120,00120,00110,00110,00110,00100,0010
−2,90,00190,00180,00180,00170,00160,00160,00150,00150,00140,0014
−2,80,00260,00250,00240,00230,00230,00220,00210,00210,00200,0019
−2,70,00350,00340,00330,00320,00310,00300,00290,00280,00270,0026
−2,60,00470,00450,00440,00430,00410,00400,00390,00380,00370,0036
−2,50,00620,00600,00590,00570,00550,00540,00520,00510,00490,0048
−2,40,00820,00800,00780,00750,00730,00710,00690,00680,00660,0064
−2,30,01070,01040,01020,00990,00960,00940,00910,00890,00870,0084
−2,20,01390,01360,01320,01290,01250,01220,01190,01160,01130,0110
−2,10,01790,01740,01700,01660,01620,01580,01540,01500,01460,0143
−2,00,02280,02220,02170,02120,02070,02020,01970,01920,01880,0183
−1,90,02870,02810,02740,02680,02620,02560,02500,02440,02390,0233
−1,80,03590,03510,03440,03360,03290,03220,03140,03070,03010,0294
−1,70,04460,04360,04270,04180,04090,04010,03920,03840,03750,0367
−1,60,05480,05370,05260,05160,05050,04950,04850,04750,04650,0455
−1,50,06680,06550,06430,06300,06180,06060,05940,05820,05710,0559
−1,40,08080,07930,07780,07640,07490,07350,07210,07080,06940,0681
−1,30,09680,09510,09340,09180,09010,08850,08690,08530,08380,0823
−1,20,11510,11310,11120,10930,10750,10560,10380,10200,10030,0985
−1,10,13570,13350,13140,12920,12710,12510,12300,12100,11900,1170
−1,00,15870,15620,15390,15150,14920,14690,14460,14230,14010,1379
−0,90,18410,18140,17880,17620,17360,17110,16850,16600,16350,1611
−0,80,21190,20900,20610,20330,20050,19770,19490,19220,18940,1867
−0,70,24200,23890,23580,23270,22960,22660,22360,22060,21770,2148
−0,60,27430,27090,26760,26430,26110,25780,25460,25140,24830,2451
−0,50,30850,30500,30150,29810,29460,29120,28770,28430,28100,2776
−0,40,34460,34090,33720,33360,33000,32640,32280,31920,31560,3121
−0,30,38210,37830,37450,37070,36690,36320,35940,35570,35200,3483
−0,20,42070,41680,41290,40900,40520,40130,39740,39360,38970,3859
−0,10,46020,45620,45220,44830,44430,44040,43640,43250,42860,4247
−0,00,50000,49600,49200,48800,48400,48010,47610,47210,46810,4641
kk0123456789
0,00,50000,50400,50800,51200,51600,51990,52390,52790,53190,5359
0,10,53980,54380,54780,55170,55570,55960,56360,56750,57140,5753
0,20,57930,58320,58710,59100,59480,59870,60260,60640,61030,6141
0,30,61790,62170,62550,62930,63310,63680,64060,64430,64800,6517
0,40,65540,65910,66280,66640,67000,67360,67720,68080,68440,6879
0,50,69150,69500,69850,70190,70540,70880,71230,71570,71900,7224
0,60,72570,72910,73240,73570,73890,74220,74540,74860,75170,7549
0,70,75800,76110,76420,76730,77040,77340,77640,77940,78230,7852
0,80,78810,79100,79390,79670,79950,80230,80510,80780,81060,8133
0,90,81590,81860,82120,82380,82640,82890,83150,83400,83650,8389
1,00,84130,84380,84610,84850,85080,85310,85540,85770,85990,8621
1,10,86430,86650,86860,87080,87290,87490,87700,87900,88100,8830
1,20,88490,88690,88880,89070,89250,89440,89620,89800,89970,9015
1,30,90320,90490,90660,90820,90990,91150,91310,91470,91620,9177
1,40,91920,92070,92220,92360,92510,92650,92790,92920,93060,9319
1,50,93320,93450,93570,93700,93820,93940,94060,94180,94290,9441
1,60,94520,94630,94740,94840,94950,95050,95150,95250,95350,9545
1,70,95540,95640,95730,95820,95910,95990,96080,96160,96250,9633
1,80,96410,96490,96560,96640,96710,96780,96860,96930,96990,9706
1,90,97130,97190,97260,97320,97380,97440,97500,97560,97610,9767
2,00,97720,97780,97830,97880,97930,97980,98030,98080,98120,9817
2,10,98210,98260,98300,98340,98380,98420,98460,98500,98540,9857
2,20,98610,98640,98680,98710,98750,98780,98810,98840,98870,9890
2,30,98930,98960,98980,99010,99040,99060,99090,99110,99130,9916
2,40,99180,99200,99220,99250,99270,99290,99310,99320,99340,9936
2,50,99380,99400,99410,99430,99450,99460,99480,99490,99510,9952
2,60,99530,99550,99560,99570,99590,99600,99610,99620,99630,9964
2,70,99650,99660,99670,99680,99690,99700,99710,99720,99730,9974
2,80,99740,99750,99760,99770,99770,99780,99790,99790,99800,9981
2,90,99810,99820,99820,99830,99840,99840,99850,99850,99860,9986
3,00,99870,99870,99870,99880,99880,99890,99890,99890,99900,9990
3,10,99900,99910,99910,99910,99920,99920,99920,99920,99930,9993
3,20,99930,99930,99940,99940,99940,99940,99940,99950,99950,9995
3,30,99950,99950,99950,99960,99960,99960,99960,99960,99960,9997
3,40,99970,99970,99970,99970,99970,99970,99970,99970,99970,9998
3,50,99980,99980,99980,99980,99980,99980,99980,99980,99980,9998
P(Z<k)=12π∫−∞ke−t2/2 dtP(Z < k) = \dfrac{1}{\sqrt{2\pi}}\displaystyle\int_{-\infty}^{k} e^{-t^2/2}\,dt
Distribución normal tipificada Densidad normal, función de distribución y área bajo la densidad a la izquierda de k, con k negativo. Recta horizontal de altura 1 y marca 0,5. 1 0,5 k 1 0,5 k