Se hizo un estudio estadístico sobre la duración de una marca de pilas. Los resultados, en horas, de una muestra de 15 pilas son: 20, 22, 25, 21, 22, 20, 23, 21, 24, 22, 24, 21, 23, 22, 21. Construye una tabla de frecuencias absolutas y relativas. a. Calcula las frecuencias absolutas y relativas acumuladas. b. ¿Qué porcentaje de pilas dura menos de 22 horas? Rta: sumo los hi < 22: 0,13 + 0,27 = 0,4 x 100% = 40% c. ¿Qué porcentaje de pilas dura menos de 21 horas? Rta: los hi < 21: 0,13 x 100% 13,33%

a) one student is chosen from classroom a, then a student is chosen from classroom b.  

step-by-step explanation:

independent events are ones in which the probability of one event does not affect the probability of the second event.

one student is chosen from classroom a; this does not affect the chances of choosing a student from classroom b.   this makes these independent events.

when one card is chosen from a standard deck and then set aside before a second card is chosen, the probability of the second card being chosen changes.   this makes them dependent events.

when one student is chosen from classroom a and then a second student is chosen from classroom a, the probability of choosing the second student changes.   this makes them dependent events.

when a letter is chosen from the alphabet and then a second letter is chosen, the probability of choosing the second letter changes.   this makes them dependent events.

c.

step-by-step explanation:

she should of added 9^2 and 12^2. that is because it is a^2+b^2=c^2. c^2 is the hypotenuse and should always be bigger than the other two numbers. which is why she should of added 9 squared and 12 squared together instead of 15 squared.