Math Is Fun Forum

ShivamS

Member

Registered: 2011-02-07

Posts: 3,648

Stats and Prob

1   What is the probability that an outcome z is less than -0.5?

0.3085

2   What is the probability that an outcome z is between -1 and 1.5?

0.7745

3   What would be the 91th percentile (P91) for such a N(0,1) distribution?

1.34

4   For a certain population diastolic blood pressure has been evaluated to have a mean value
of 75, a 10th percentile (P10) of 55, an 80th percentile (P80) of 90, and a range of 60. What
can we say for sure about diastolic blood pressure in that population?

Third quartile can't be more than 90.

According to a recent article in the journal "Appetite," 70% of 2 to 5 year old children
living in the US suffer from food neophobia. We choose at random five 2 to 5 year old
children living in the US.

5   What is the probability that at least four of the chosen children suffer from food
neophobia?

0.528

6   What is the probability that the number of children suffering from food neophobia
among the five chosen is between one and three, both inclusive?

0.6

According to a recent article in the journal "Environmental Health Perspectives," the
amount of soil ingested in one day by infants living in a particular town is a random
variable with a normal distribution with mean 20 g and variance 4. Assume that is
really the case.

7   What is the probability that an infant chosen at random from that town will ingest
more than 25 grams of soil in one day?

0.8944

8   What is the probability that an infant chosen at random from that town will ingest
less than 15 grams of soil in one day?

0.9876

9   Now assume that we chose at random 4 infants from that town. What is the
probability that none of them will ingest more than 25 grams of soil in one day?

0.9754

10   Suppose we flip a fair coin 10 times. What is the probability that we will get heads
every single time? 0.001

11   Now suppose we flip a coin that has heads on both sides. What is now the
probability that we will get heads every single time?   1, obviously.

A clinic has four departments, headed by doctor A, doctor B, doctor C, and doctor D,
respectively. Dr. A's department is treating 10 patients at this time, Dr. B's department is
treating 2 patients, Dr. C's department is treating 5 patients, and Dr. D's department is
treating 4 patients.
A patient from the clinic is chosen to be entered in a new clinical trial after informed
consent. The procedure to choose such a patient is the following: first a department in
the clinic is chosen at random, and then a patient from the chosen department is chosen
also at random.

12   What is the probability that John R, a patient treated by Dr. C, will be chosen to
enter the clinical trial?  0.05

13   What is the probability that Mary H., a patient in Dr. A's department, will be
chosen to enter the clinical trial?

0.025

One or two might be wrong so I need someone to check them. Reviewing for the final exam (our prof. gave me many pages like this). Thank-you in advance.

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Stats and Prob

Hi;

1) Is correct.

2) Is right.

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

ShivamS

Member

Registered: 2011-02-07

Posts: 3,648

Re: Stats and Prob

Okay, thanks. I realize they are a lot though.

anonimnystefy

Real Member

From: Harlan's World

Registered: 2011-05-23

Posts: 16,049

Re: Stats and Prob

5 is correct and 6 is incorrect. I will check the others.

---

“Here lies the reader who will never open this book. He is forever dead.
“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Stats and Prob

10) Is a good rounding of the answer.

11) Is correct.

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

ShivamS

Member

Registered: 2011-02-07

Posts: 3,648

Re: Stats and Prob

Thanks.

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Stats and Prob

7) Needs work.

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

anonimnystefy

Real Member

From: Harlan's World

Registered: 2011-05-23

Posts: 16,049

Re: Stats and Prob

8, too.

---

“Here lies the reader who will never open this book. He is forever dead.
“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.

ShivamS

Member

Registered: 2011-02-07

Posts: 3,648

Re: Stats and Prob

I did it again and got 0.0062. 7 that is. Now I will do 8. Getting 0.0062 for 8 too!

Last edited by Shivamcoder3013 (2013-06-05 01:09:11)

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Stats and Prob

That is correct!

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

ShivamS

Member

Registered: 2011-02-07

Posts: 3,648

Re: Stats and Prob

And I am getting 0.0062 for 8 as well.

anonimnystefy

Real Member

From: Harlan's World

Registered: 2011-05-23

Posts: 16,049

Re: Stats and Prob

12 and 13 are correct!

---

“Here lies the reader who will never open this book. He is forever dead.
“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Stats and Prob

8) Is correct now too.

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

ShivamS

Member

Registered: 2011-02-07

Posts: 3,648

Re: Stats and Prob

Thanks everyone, is 8 correct now? And just saw Stefy say that 6 is wrong. Now I am getting for it (as there are two answers and I took the average). So many mistakes due to carelessness...

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Stats and Prob

Hi;

9) Is good!

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

anonimnystefy

Real Member

From: Harlan's World

Registered: 2011-05-23

Posts: 16,049

Re: Stats and Prob

Hm? There is only one onswer for 6.

---

“Here lies the reader who will never open this book. He is forever dead.
“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.

ShivamS

Member

Registered: 2011-02-07

Posts: 3,648

Re: Stats and Prob

0.028 + 0.132 + 0.309 = 0.469 and = 0.472 – 0.002 = 0.470

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Stats and Prob

12) Looks to be a good rounding.

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

ShivamS

Member

Registered: 2011-02-07

Posts: 3,648

Re: Stats and Prob

Thank-you both very much.

anonimnystefy

Real Member

From: Harlan's World

Registered: 2011-05-23

Posts: 16,049

Re: Stats and Prob

3 is correct.

---

“Here lies the reader who will never open this book. He is forever dead.
“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Stats and Prob

Again, what was your answer for 6?

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

anonimnystefy

Real Member

From: Harlan's World

Registered: 2011-05-23

Posts: 16,049

Re: Stats and Prob

The exact answer for 6 is 0.46935 .

---

“Here lies the reader who will never open this book. He is forever dead.
“Taking a new step, uttering a new word, is what people fear most.” ― Fyodor Dostoyevsky, Crime and Punishment
The knowledge of some things as a function of age is a delta function.

ShivamS

Member

Registered: 2011-02-07

Posts: 3,648

Re: Stats and Prob

0.4695 as an average of 0.470 and 0.469

bobbym

bumpkin

From: Bumpkinland

Registered: 2009-04-12

Posts: 109,606

Re: Stats and Prob

I am not getting that for 6?!

---

In mathematics, you don't understand things. You just get used to them.
If it ain't broke, fix it until it is.
Always satisfy the Prime Directive of getting the right answer above all else.

ShivamS

Member

Registered: 2011-02-07

Posts: 3,648

Re: Stats and Prob

P(1 ≤ X ≤ 3) = P(X=1) + P(X=2) + P(X=3) = 0.028 + 0.132 + 0.309 = 0.469
Similarly, P(1 ≤ X ≤ 3) = P(X ≤ 3) – P(X ≤ 0) = 0.472 – 0.002 = 0.470