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Bunuel
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Total number of options for units digit = {1,3,5,7,9} = 5
Total options for first digit = exclude 2 {digit at units place, 0} = 10 - 2 = 8
Total number of possibilities = 8*8*7*6*5

Total favorable options = 1 _ _ _ 9 = 8*7*6

P(E) = 1/(8*5) = 1/40

Ans: B
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Hey, can some one elaborate this more?

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Lipun
Total number of options for units digit = {1,3,5,7,9} = 5
Total options for first digit = exclude 2 {digit at units place, 0} = 10 - 2 = 8
Total number of possibilities = 8*8*7*6*5

Total favorable options = 1 _ _ _ 9 = 8*7*6

P(E) = 1/(8*5) = 1/40

Ans: B


What is total no of possibilities here?

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Abi1995

What is total no of possibilities here?

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Hi Abi1995,

The total number possibilities here is defined as the set of -
a) five digit,
b) odd numbers,
c) having 5 distinct digits.
all the above constraints are grouped by AND logic.

Using constraint (b), the number of possibilities for units place is reduced to 1,3,5,7,9. Total = 5
So, now the number is : {A} _ _ _ {1,3,5,7,9}
Number of options for A is {1,2,3,4,5,6,7,8,9} - {digit at units place} = 8
The middle 3 digits can be take any values excluding the digit at units place and the digit at A = 8*7*6

So, total possibilities = 8*8*7*6*5

Does it help?

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Lipun
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There is no restriction saying that digits not be reused so shouldn't the total no of odd digit nos be 8*9*9*9*5?

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I try to solve this problem following this way but can't find out where i made a mistake...
my approach:

The five digit number is =1,3,5,7,9
Question says us that leftmost digit is 1 and unit digit is 9 .

So this two digit is fixed and we have 3 most odd digit from 1 to 9 except 1 and 9 that may rearrange by 3! ways.

So required probability is=3!/5!
=1/20.
where is my mistake? I can't find out.

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