Mathematics

Probability Distributions

488 Questions

Probability distributions describe the likelihood of different outcomes in a statistical experiment. Key topics include calculating confidence intervals, understanding Type II errors, and working with the standard normal distribution. These concepts are frequently tested in mathematics and statistics sections of various competitive exams.

Standard normal distributionType II error probabilityConfidence interval interpretationPoisson distributionProbability density function

Probability Distributions Questions

Multiple choice business maths random variables and probability distribution poisson distribution poisson distrubution probability distributions

Cycle tyres are supplied in lots of $10$ and there is a chance of $1$ in $500$ to be defective. Using poisson distribution, the approximate number of lots containing no defectives in a consignment of $10,000$ lots if $e^{-0.02}=0.9802$ is

  1. $9980$
  2. $9998$
  3. $9802$
  4. $9982$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Here $\lambda = \cfrac{1}{500}\times 10 = 0.02$
Thus probability that  lot is not defective is $=P(X=0)=\cfrac{e^{-0.002}(.0020^0}{0!}=e^{-.002}=0.9802$
Hence number of no defective lots out of $10,000$ is $=.9802\times 10,000=9802$

Multiple choice business maths random variables and probability distribution poisson distribution poisson distrubution probability distributions

The chance of a traffic accident in a day attributed to a taxi driver is $0.001$. Out of a total of $1000$ days the number of days with no accident is

  1. $1000\times e^{-1}$
  2. $1000\times e^{-0.1}$
  3. $1000\times e^{-0.001}$
  4. $1000\times e^{-0.0001}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Here $\lambda = 0.001$
Hence number of day out of 1000 days without accident is $1000\times P(X=0)=1000\times e^{-0.001}$

Multiple choice business maths random variables and probability distribution poisson distribution poisson distrubution probability distributions

A manufacturer of cotter pins knows that $5$% of his product is defective. If he sells cotter pins in boxes of $100$ and guarantees that not more than $10$ pins will be defective, the approximate probability that a box will fail to meet the guaranteed quality is

  1. $\displaystyle \frac{e^{-5}5^{10}}{ 10!}$
  2. $1-\displaystyle \sum _{x=0}^{10}\frac{e^{-5}5^{x}}{ x!}$
  3. $1-\displaystyle \sum _{x=0}^{\infty }\frac{e^{-5}5^{x}}{ x!}$
  4. $\displaystyle \sum _{x=0}^{\infty }\frac{e^{-5}5^{x}}{ x!}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

we are given $n=100$
let $p=$ probability of a defective bulb $=5$%$=0.05$
$\therefore m=$ mean number of defective bulbs in a box of $100=np=100\times 0.05=5$
Since p is small , we can use poison's distribution.
Probability of $x$ defective bulbs in a box of $100$ is
$\displaystyle P\left( X=x \right) =\frac { { e }^{ -m }{ m }^{ x } }{ x! } =\frac { { e }^{ -5 }{ 5 }^{ x } }{ x! } ,x=0,1,2...$
Probability that is box will fail to meet the guarented quality is $\displaystyle P\left( X>10 \right) =1-P\left( X\le 10 \right) =1-\sum _{ x=0 }^{ 10 }{ \frac { { e }^{ -5 }{ 5 }^{ x } }{ x! }  } =1-{ e }^{ -5 }\sum _{ x=0 }^{ 10 }{ \frac { { 5 }^{ x } }{ x! }  } $

Multiple choice business maths random variables and probability distribution poisson distribution poisson distrubution probability distributions

The number of accidents in a year attributed to a taxi driver in a city follows Poisson distribution with mean $3$. Out of $1000$ taxi drivers, the approximate number of drivers with no accident in a year given that $e^{-3}=0.0498$ is

  1. $4.98$
  2. $49.8$
  3. $498$
  4. $4.8$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Here $\lambda = 3$
Hence Number of drivers with no accident out of 1000 is $=1000\times P(X=0)=1000\times e^{-3}=1000\times 0.0498=49.8$

Multiple choice business maths random variables and probability distribution poisson distribution poisson distrubution probability distributions

A manufacturing concern employing a large number of workers finds that, over a period of time, the average absentee rate is $2$ workers per shift. The probability that exactly $2$ workers will be absent in a chosen shift at random is

  1. $\displaystyle \frac{e^{-2}2^{2}}{ 2!}$
  2. $\displaystyle \frac{e^{-2}2^{3}}{3!}$
  3. $e^{-2}$
  4. $e^{-3}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

By using Poisson distribution, 
$ P(x;\mu)=\dfrac { { e }^{ -\mu }{ \mu }^{ x } }{ x! } $
$ \mu $: The mean number of successes that occur in a specified region(parameter)
x: The actual number of successes that occur in a specified region.
P(x; $ \mu $): The Poisson probability that exactly x successes occur in a Poisson experiment, when the mean number of successes is $ \mu $
Here,$ \mu $  = 2 
x = 2 (exact 2 workers)
$ P(2;2)=\dfrac { { e }^{ -2 }{ 2 }^{2 } }{ 2! } $

Multiple choice business maths random variables and probability distribution poisson distribution poisson distrubution probability distributions

A manufacturer who produces medicine bottles finds that $0.1$% of the bottles are defective. The bottles are packed in boxes containing $500$ bottles. A drug manufacturer buys $100$ boxes from the producer of bottles. Using poisson distribution,the number of boxes with at least one defective bottle is

  1. $100(1-e^{-0.1})$
  2. $100(1-e^{-0.5})$
  3. $100(1-e^{-0.05})$
  4. $100(1-e^{-0.01})$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Here $\lambda = \cfrac{0.1}{100}\times 500=0.5 $
Hence number of boxes out of 100 which contain at least one defective bottle is,
$=100\left(1-P(X=0)\right)=100\left(1-e^{-0.5}\right)$ 

Multiple choice business maths random variables and probability distribution poisson distribution poisson distrubution probability distributions

Suppose $2$% of the people on an average are left handed. The probability of 3 or more left handed among 100 people is

  1. $3e^{-2}$
  2. $4e^{-2}$
  3. $1-5e^{-2}$
  4. $5 e^{-2}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Here P.D parameter $\lambda = \cfrac{2}{100}\times 100=2$
Hence probability that 3 or more people are left handed is $=1-P(X=0)-P(X=1)-P(X=2)$
$=1-e^{-2}-\cfrac{e^{-2}2}{1!}-\cfrac{e^{-2}2^2}{2!}=1-5e^{-2}$

Multiple choice business maths random variables and probability distribution poisson distribution poisson distrubution probability distributions

Suppose there is an average of $2$ suicides per year per $50,000$ population. In a city of population $1,00,000$, the probability that in a given year there are, zero suicides is

  1. $1.e^{-2}$
  2. $1-e^{-2}$
  3. $e^{-4}$
  4. $1-e^{-4}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

P.D parameter $\lambda = \cfrac{2}{50000}\times 100000 = 4$
Thus probability that in a year there is no suicide is $=P(X=0)=e^{-4}$

Multiple choice business maths random variables and probability distribution poisson distribution poisson distrubution probability distributions

Suppose on an average $5$ out of $2000$ houses get damaged due to fire accident during summer. Out of $10,000$ houses in a locality, the probability that exactly $10$ houses will get damaged during summer is

  1. $\displaystyle \frac{e^{-5}5^{10}}{ 10!}$
  2. $\displaystyle \frac{e^{-10}10^{10}}{ 10!}$
  3. $\displaystyle \frac{e^{-25}25^{10}}{10!}$
  4. $\displaystyle \frac{e^{-15}15^{10}}{10!}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Here P.D parameter $\lambda = \cfrac{5}{2000}\times 10000=25$
Hence probability that exactly 10 houses will get damaged $=P(X = 10) = \cfrac{e^{-25}(25)^{10}}{10!}$

Multiple choice business maths random variables and probability distribution poisson distribution poisson distrubution probability distributions

A manufacturer who produces medicine bottles finds that $0.1$$\%$ of the bottles are defective. The bottles are packed in boxes containing $500$ bottles. A drug manufacturer buys $100$ boxes from the producer of bottles. Using Poisson distribution, the number of boxes with no defective bottle is

  1. $100\times e^{-0.1}$
  2. $100\times e^{-0.5}$
  3. $100\times e^{-0.05}$
  4. $100\times e^{-0.01}$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

$\displaystyle p=\frac { 0.1 }{ 100 } =0.001,n=500\ \lambda =np=500\times 0.001=0.5\ N=100$
We know that $\displaystyle p\left( r \right) =e^{ -1 }\frac { { \lambda  }^{ r } }{ r! } $
Number of boxes containing no defective bottle 
$\displaystyle =N.P.\left( r=0 \right) =1000\times { e }^{ 0.5 }\frac { \left( 0.5 \right) ^{ 0 } }{ 0! } =1000\times { e }^{ -0.5 }$

Multiple choice business maths random variables and probability distribution poisson distribution poisson distrubution probability distributions

A company knows on the basis of past experience that $2$% of its blades are defective. The probability of having $3$ defective blades in a sample of $100$ blades if $e^{-2}=0.1353$ is

  1. $0.1353$
  2. $0.1804$
  3. $0.2706$
  4. $0.3606$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Here P.D parameter $\lambda = \cfrac{2}{100}\times 100=2$
Hence number of probability that 3 blade are defective is $=P(X=3)=\cfrac{e^{-2}(2)^3}{3!}=\cfrac{4}{3}e^{-2}=\cfrac{4}{3}\times .1353=.1804$

Multiple choice business maths random variables and probability distribution poisson distribution poisson distrubution probability distributions

On the average a submarine on patrol sights $6$ enemy ships per hour. Assuming the number of ships sighted in a given length of time is a poisson variate, the probability of sighting $4$ ships in the next two hours is

  1. $\displaystyle \frac{e^{-12}12^{4}}{ 4!}$
  2. $\displaystyle \frac{e^{-4}12^{12}}{ 3!}$
  3. $\displaystyle \frac{e^{-6}12^{4}}{ 4!}$
  4. $\displaystyle \frac{e^{-3}12^{2}}{ 4!}$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

By using Poisson distribution, 
$ P(x;\mu)=\dfrac { { e }^{ -\mu }{ \mu }^{ x } }{ x! } $
$ \mu $: The mean number of successes that occur in a specified region(parameter)
x: The actual number of successes that occur in a specified region.
P(x; $ \mu $): The Poisson probability that exactly x successes occur in a Poisson experiment, when the mean number of successes is $ \mu $
the average a submarine on patrol sights 6 enemy ships per hour, so for 2 hours
Here, $ \mu =  6 \times 2 = 12 $
x = 4 ( ships)
$ P(4;12)=\dfrac { { e }^{ -12 }{12 }^{4 } }{ 4! }$

Multiple choice business maths random variables and probability distribution poisson distribution poisson distrubution probability distributions

Patients arrive randomly and independently at a Doctor's room from 8 AM at an average rate of one in 5 minutes. The waiting room can accommodate 12 persons. The probability that the room will be full when the doctor arrives at 9AM is

  1. $\displaystyle \frac{{e}^{-12}(12)^{12}}{ 12!}$
  2. $\displaystyle \sum _{{x}=0}^{11}\frac{{e}^{-12}(12)^{{x}}}{ x!}$
  3. $1-\displaystyle \sum _{{x}=0}^{11}\frac{{e}^{-12}(12)^{{x}}}{ x!}$
  4. $1-\displaystyle \sum _{{x}=0}^{\infty }\frac{{e}^{-12}(12)^{{x}}}{ x!}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Random Arrival process is a Poisson process
Given by
$P(k) = \dfrac{e^{-\lambda} \lambda^x}{x!}$
$given, \lambda = 1/5 min^{-1}= 12 s^{-1}$
Room is not full, if No.of patients $< 12$
Hence 
$P$(room is full) $= 1 - (P(1)+ . . . . +P(11))$
$=1-\displaystyle \sum _{{x}=0}^{11}\frac{{e}^{-12}(12)^{{x}}}{ x!}$

Multiple choice business maths random variables and probability distribution poisson distribution poisson distrubution probability distributions

On an average, a submarine on patrol sights $6$ enemy ships per hour. Assuming the number of ships sighted in a given length of time is a Poisson variate, the probability of sighting at least two ships in the next $20$ minutes is

  1. $1-e^{-2}$
  2. $1-2e^{-2}$
  3. $1-3e^{-2}$
  4. $1-4e^{-2}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The probability of sighting at least two ships
=1-(Probability of sighting atmost 1 ships)
$=1-e^{-\lambda}-\dfrac{\lambda^{1}e^{-\lambda}}{1!}$
Here $\lambda=2$
Hence 
$P=1-e^{-\lambda}-\dfrac{\lambda^{1}e^{-\lambda}}{1!}$
$=1-e^{-2}-2e^{-2}$
$=1-3e^{-2}$.

Multiple choice business maths random variables and probability distribution poisson distribution poisson distrubution probability distributions

If $X$ is a Poisson's variate such that $P(X=1)=3P(X=2)$, then find the variance of $X$.

  1. $\cfrac 38$
  2. $\cfrac 13$
  3. $\cfrac 23$
  4. $\cfrac 54$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation
Fact:  Poisson distribution is $P(X=r)=\dfrac{e^{-\lambda}\lambda ^r}{r!}$

Now given $P(X=1)=3P(X=2)$

$\Rightarrow \dfrac{e^{-\lambda}\lambda}{1!}=3\cdot \dfrac{e^{-\lambda} \lambda^2}{2!}$

$\Rightarrow \lambda =\dfrac{2}{3}=$ Variance