# Statistics

**Discrete Mathematics**Level 4

A jar contains 7 white marbles and 3 blue marbles. Given that the 4 marbles are chosen from the jar at the same time, find the standard deviation of the number of the blue marbles chosen. If the standard deviation can be written as \( \dfrac{ \sqrt{a} } { b} \) where \( a \) and \( b \) are coprime positive integers and \( a \) is square-free, then what is \(a+b \)?