Question

A test for the level of potassium in the blood is not perfectly precise. Moreover, the actual level of potassium in a person's blood varies slightly from day to day. Suppose that repeated measurements for the same person on different days vary normally with .

Answer 1

Standard deviation= 0.2.

Answer 2

a) Julie's potassium level is measured once. The result is x-bar = 3.4. Give a 90% confidence interval for her mean potassium level.
b) If three measurements were taken on different days and the mean result is x = 3.4, what is a 90% confidence interval for Julie's mean blood potassium level?
c) How large a sample of Julie's potassium levels in the previous exercise would be needed to estimate her mean within 0.06 with 95% confidence?

Answer 3

I ONLY NEED C @jim_thompson5910

Answer 4

@amistre64 help with just C?

Answer 5

My answers for a and b:

(a)

x bar = 3.
n = 1
std = 0.2
z value = 1.645

3 plus/minus 1.645 (0.2/(sqrt1))

Interval = [3.07, 3.73]

(b)

x bar = 3.
n = 3
std = 0.2
z value = 1.645

3 plus/minus 1.645 (0.2/(sqrt3))

Interval : [3.21, 3.59]

(c)

Answer 6

@jim_thompson5910 i only need c;)

Answer 7

E = margin of error

E = C*sigma/sqrt(n)

0.06 = 1.96*0.2/sqrt(n)

solve for n

Answer 8

oh ok

Answer 9

tell me what you get

Answer 10

0.06 = .392/sqrt(n)

Answer 11

keep going

Answer 12

sqrt n = 0.15306122449 ?

Answer 13

0.15306122449 = sqrt(n)
?

Answer 14

no something is off

Answer 15

idk

Answer 16

oh it should be 1/sqrt(n) = 0.15306122449

Answer 17

ok then?

Answer 18

im not asure what to do next

Answer 19

solve for n

Answer 20

sqrt(n) = 0.15306122449

Answer 21

no it's 1/sqrt(n) = 0.15306122449

Answer 22

.39123039821

Answer 23

?

Answer 24

you then multiply both sides by sqrt(n) to get

1 = 0.15306122449 *sqrt(n)

Answer 25

ok

Answer 26

keep going

Answer 27

so its the sqrt of 0.15306122449

Answer 28

no

Answer 29

that times the square root of n

Answer 30

?

Answer 31

solve

1 = 0.15306122449 *sqrt(n)

for n

Answer 32

so divide sqrt n?

Answer 33

1/sqrt n = 0.15306122449

Answer 34

?

Answer 35

but that gets you back where you started from

Answer 36

so at this point you're going in circles

Answer 37

ugh

Answer 38

idk aht to do

Answer 39

why not divide both sides by 0.15306122449 instead of sqrt(n)

Answer 40

1 = 0.15306122449 *sqrt(n)

Answer 41

6.53333333332 = sqrt n

Answer 42

?

Answer 43

good

Answer 44

last step?

Answer 45

42.6844444443?

Answer 46

now round to the nearest integer

Answer 47

42.7

Answer 48

because n = sample size (which is a whole number)

Answer 49

43

Answer 50

?

Answer 51

you nailed it, that's the min sample size needed