SOLUTION: I am a salesperson & I close on 70% of all my sales. If I call on 4 sales, what is the probability that I will close on 3 of the 4 sales?

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Question 664071: I am a salesperson & I close on 70% of all my sales. If I call on 4 sales, what is the probability that I will close on 3 of the 4 sales?
Found 3 solutions by jim_thompson5910, Theo, ikleyn:
Answer by jim_thompson5910(35256) About Me  (Show Source):
You can put this solution on YOUR website!
Use the binomial probability distribution formula P(X = k) = (n C k)*(p)^(k)*(1-p)^(n-k)

In this case, k = 3, n = 4 and p = 0.7

P(X = k) = (n C k)*(p)^(k)*(1-p)^(n-k)
P(X = 3) = (4 C 3)*(0.7)^(3)*(1-0.7)^(4-3)
P(X = 3) = (4 C 3)*(0.7)^(3)*(0.3)^(4-3)
P(X = 3) = (4)*(0.7)^(3)*(0.3)^1
P(X = 3) = (4)*(0.343)*(0.3)
P(X = 3) = 0.4116

So the probability is 0.4116, which is a 41.16% chance.

Answer by Theo(13342) About Me  (Show Source):
You can put this solution on YOUR website!
the probability that you will close on a sale is .7
if you call on 4 sales, the probability that you will close on exactly 3 of them is equal to C(4,3)*.7^3*.3^1 which is equal to .4116
all the probabilities are shown in the following table
x       c(4,x)  .7^x    .3^(4-x)  p(x)
0	1.00	1.00	0.0081	  0.0081
1	4.00	0.70	0.027	  0.0756
2	6.00	0.49	0.09	  0.2646
3	4.00	0.34	0.3	  0.4116
4	1.00	0.24	1	  0.2401

c(4,x) is the combination formula for selecting x items out of 4.
.7^x is the probability of making a sale raised to the x power.
.3^(4-x) is the probability of not making a sale raised to the (4-x) power
p(x) is equal to c(4,x) * .7^x * .3^(4-x)
that's the probability of getting x out of 4.
your solution is getting 3 out of 4 sales to be successful.

Answer by ikleyn(52957) About Me  (Show Source):
You can put this solution on YOUR website!
.
I am a salesperson & I close on 70% of all my sales. If I call on 4 sales, what is the probability
that I will close on 3 of the 4 sales?
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        In the post by @Theo, there are too many words and too many excessive calculations.
        It is not a mathematical style solving and not a good style teaching.
        I came to provide a solution in the form as it should be done and presented.


This problem is on Binomial distribution.

The number of trials is 4.  The probability of a success at each individual trial is p = 0.7.

They want you find the probability of having 3 success in 4 trials.


Use the formula for binomial distribution


    P(n=4; k=3; p=0.7) = C%284%2C3%29%2Ap%5E3%2A%281-p%29%5E1,


where  C(4.3) = 4%21%2F3%21 = %281%2A2%2A3%2A4%29%2F%281%2A2%2A3%29 = 4 is the binomial coefficient.

The formula gives

    P = 4%2A0.7%5E3%2A0.3 = 0.4116.


ANSWER.  The probability to close 3 sales of 4 sales in this problem is 0.4116.

Solved.

As you solve your problems on Binomial distribution, when you treat this given problem
among many others problems of this topic, two moments are important:

        (a)  to recognize from the text that this given problem is on Binomial distribution,

    and

        (b)  to apply an appropriate formula of the binomial distribution.

These are the key.   The rest is pure mechanical job for a calculator.