Question

Average: 60
Standard diviation: 11.35
What is the probability that a randomly selected monthly cell phone bill is between $45 and $70?

Answer 1

so.... same concept as last time; but we want the probability from defined points

Answer 2

z1 = (45 - 60)/11.35

z2 = (70-60)/11.35

Answer 3

if we use the table i posted in the last one; we would simply then subtract: z2 - z1

Answer 4

or rather tthe probability values associated with z2 from those of z1

Answer 5

z1 = -1.32
P(z1) = .4066

z2 = 0.88
P(z2) = .8106

Answer 6

P(z2) - P(z1) = .404 then if i did it right

Answer 7

shouldn't it be .3106? for z2

Answer 8

no, since it is to the right of the mean; z is positive; it is greater than .5 but let me dbl chk to see that I got the right p-value for it

Answer 9

z=.88 lines up with .8 on the left and .08 from the top to meet at .8106

Answer 10

on your table it appearts that they measure FROM the mean so you need to add .5 to it

Answer 11

<---------(0).........(.88) ----------->
.5 +.3108

Answer 12

.404 wasn't the answer, i can't figure it out

Answer 13

are the zscores good then?

Answer 14

i think so?

Answer 15

z2 = .88 ; 10/11.35

z1 = -1.32; -15/11.35

<--------(-1.32).............(0).................(.88)--------->
.4066 .5 +.3108

Answer 16

might be .0934 if i read the wolf right

Answer 17

.81056-.0934 then

Answer 18

cannot type today

Answer 19

.7172 perhaps?

Answer 20

.9066 - .5 = .4066 from the mean, which if i see it right is good; the other is .3108 from the mean

.4066
+.3108
-------
.7174 is the total probability to the left and right of the mean ... i was just intepreting it wrong