20. There are 252 identical plastic chips numbered 1 through 252 in a box. What

Question

20. There are 252 identical plastic chips numbered 1 through 252 in a box. What is the probability of reaching into the box and randomly drawing the chip numbered 81? Express your answer as a simplified fraction or a decimal rounded to four decimal places.

30. Customer account "numbers" for a certain company consist of 2 letters followed by 4 numbers.

Step 1 of 2: How many different account numbers are possible if repetitions of letters and digits are allowed?

Step 2 of 2: How many different account numbers are possible if repetitions of letters and digits are not allowed?

Explanation / Answer

(20) required probability=1/252

probability of selection of any numbered chips will be same and that of numbered 81

(30) there are 26 letters (A to Z)and 10 digits( 0 to 9)

step 1: answer is =6760000

first letter can be from 26 letter and its way of selection=26

second letter selection=26( repition is allowed)

similary first to fourth each of number selection way=10

so required way=26*26*10*10*10*10=6760000

step 2: answer=3276000

first letter can be from 26 letter and its way of selection=26

second letter selection from the remining 25 letter =25( repition is not allowed)

similary first number selection way=10

number of way to select second number =9

number of way to select third number =8

number of way to select founth number =7

requied way=26*25*10*9*8*7=3276000

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