Discussion Forum

1)

 The probability distribution of a  random variable  X is given below

 

If  mean of X is 4.2,  then a and b are respectively equal to 

Answer:

Option C

Explanation:

 We have, 

$\sum P_{i}=a+a+a+b+b+b+0.3$

$\Rightarrow$     $1=3a+2b+0.3$

$\Rightarrow$      $3a+2b=0.7$  .........(i)

$\sum P_{i}x_{i}=a+2a+3a+4b+5b+1.8$

$\Rightarrow$    $4.2=6a+9b+1.8$

$\Rightarrow$    $2a+3b=0.8$       .........(ii)

 Solving Eqs,(i) and (ii), we get

  a=0.1, b=0.2