Let the mean and variance of 7 observations 
, be 8 and 16 respectively. Two numbers are chosen from 
one after another without replacement, then the probability, that the smaller number among the two chosen numbers is less than 4 , is :
Text Solution
Verified by ExpertsD
Mean 
gives 
.
Variance 
gives 
.
Solving: 
(since 
).
Set becomes 
.
Total ways to choose 2 numbers 
.
Favorable cases (smaller 
): smaller 
gives 5 pairs, smaller 
gives 4 pairs, smaller 
gives 3 pairs.
Total favorable 
.
Probability 
.
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