Question

A bag contains 5 red balls and some blue balls. If the probability of drawing a blue ball is double that of a red ball, find the number of blue balls in the bag.

Answer 1

Number of red balls in a bag = 5
Suppose the number of blue balls in the bag = x `" "|ul({:(R,B),(5,x):})|`
`therefore" Total number of balls in the beg"=5+x`
`therefore" P(red ball)"=(5)/(5+x)`
`P"(blue ball)"=(x)/(5+x)`
Now, P(blue ball) = 2 P(red ball) (given)
`rArr" "(x)/(5+x)=2xx(5)/(5+x)`
`rArr" "x=10`
Therefore, the number of blue balls in the bag are 10.