S2 edexcel question- really need help

perkyDani

a large dental practice wishes to investigate level of satisfaction of paitient

a)suggest suitable sampling frame
b)identify sampling units
c)state one disadv and one adv of using a sample survey rather than a census
d) suggest a problem that might arise with the sampling frame when selecting patients
(a) The list of patients registered at the practice.
(b) The patients.
(c) Disadvantage: less accurate. Advantage: cheaper, faster, easier.
(d) Some patients on the list could have moved away or died. Some might not be willing to answer questions.

why might the population and the sampling frame not be the same?

Say your population is "Customers of WH Smith". There is no list of such people, so you have to choose a smaller sampling frame - for example, the customers of a particular branch on a particular day.

Reply 3

nageen

1

1. The random variables R, S and T are distributed as follows R ∼ B(15, 0.3), S ∼ Po(7.5), T ∼ N(8, 22).
Find
(a) P(R = 5),
(b) P(S = 5),
(c) P(T = 5).

can someone help me with part (c) plz i really need help.

Reply 4

nageen

1. The random variables R, S and T are distributed as follows R ~ B(15, 0.3), S ~ Po(7.5), T ~ N(8, 22).
Find
(a) P(R = 5),
(b) P(S = 5),
(c) P(T = 5).

can someone help me with part (c) plz i really need help.

Short answer (enough for the exam):
0, because T is a continuous RV.

Long answer:
If X is a continuous RV then, for any a and b with a <= b,

P(a <= X <= b) =

\int_a^b

f(x) dx

where f is the pdf of X. So

P(X = a)
= P(a <= X <= a)
=

\int_a^a

f(x) dx
= 0

because the area represented by the integral is 0.

Reply 5

standardis 5-8 over root 22

then 1 minus the fi answer from the table :smile:

i get 0.2643

Reply 6

Jonny W

Short answer (enough for the exam):
0, because T is a continuous RV.

Long answer:
If X is a continuous RV then, for any a and b with a <= b,

P(a <= X <= b) =

\int_a^b

f(x) dx

where f is the pdf of X. So

P(X = a)
= P(a <= X <= a)
=

\int_a^a

f(x) dx
= 0

because the area represented by the integral is 0.

um

its normally distributed matey

Reply 7

Finn

um

its normally distributed matey

A normal distribution is an example of a continuous distribution.

Reply 8

er no your answer is wrong so is mine though i didnt realise it was just 5, though less than or equal to, if its just five its the probability less than or equal to 5 minus probability less than or equal to 4.

Reply 9

Finn

er no your answer is wrong so is mine though i didnt realise it was just 5, though less than or equal to, if its just five its the probability less than or equal to 5 minus probability less than or equal to 4.

What is the probability that a randomly selected person is EXACTLY six feet tall?

Reply 10

i get 0.2643 minus 0.1977 = 0.0666 i think thats the right answer

Reply 11

no P T=5 is greater than 4.5 and less than5.5 using continuity so there is a probability as ive worked out

0.0666

Reply 12