Four different positive integers less than 10 are chosen randomly what is the probability that their sum is odd?

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1.Quant Question Of The Day : 19
2. Quant Question Of The Day : 18

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1.Divisibility Rule of a Number (Divisibility Test)
2. Divisors of a Number ( Number of Divisors of a number)


  1. Mayank Khanna

    We know that odd+ even = odd. So it means, we have to choose some combination of odd and even. Now, as we see 2 odd + 2 even such as 2+4+5+7= 18 , 6+8+3+9= 26 gives even answer. ( As numbers are small so I just calculated the sum . However, if the numbers are big is there any method or rule for 4 numbers , please mention in reply sir) .
    By observing we find , we have to keep 3 number of odd and 1 of even or 3 of even and 1 of odd. So we try and probability is
    (3/5.1/5 )+(3/5+1/5)
    As we consider both cases. Now we have 6/25.
    Hence 6/25.
    I am not sure of my approach as it works well with small number but when big numbers are there it won’t and secondly it took me more than 2 minutes to do it.

  2. Mayank Khanna

    I followed the rule that odd+even=odd. Till 10 we have to choose 4 numbers, so choose it in the manner as either 3 odd and 1 even or 3 even and 1 odd. Now, we have
    (3/5).(i/5)+ (3/5).(1/5)= 6/25 or 0.24

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