i have a probability question

Question

items sold                                  Frequency

 

 

     0                                              6

     1                                              8

     2                                              3

     3                                              2

     4                                              1

 

Find the probability that she sells the following:

a) exactly 1 item

b) more than 2 items

c) At least 1 item

d) At most 3 items

 

Answer 1

 

From the given table , total number of instances that none or at least one item has been sold = sum of all the frequencies = 20. So this will be my denominator for all the probability calculation

 

a) exactly one item sold = 8  times

so probability that exactly one item sold is 8/20 = 2/5

 

b) more than 2 items implies either 3 or 4 items sold which is (2+1) = 3 times 

so probability that more than 2 items sold = 3/20

 

c) at least 1 item sold implies either 1, 2 3 or 4 items sold. 

probability that at least 1 item sold = 1 - probability that no items sold

which is 1 - 6/20 = 14/20 =7/10

 

d) at most 3 items implies that no item or 1 ,2 or 3 items sold 

is same as 1 - probability that 4 itemss sold 

which is 1 -1/20 = 19/20