Solution:

It is given that the absolute number of red balls = 5

Let the all out number of blue balls = x

In this way, the all out no. of balls = x+5

P(E) = (Number of good results/Total number of results)

∴ P (drawing a blue ball) = [x/(x+5)] — – (I)

Also,

P (drawing a red ball) = [5/(x+5)] — – (I)

From condition (I) and (ii)

x = 10

In this way, the all out number of blue balls = 10