Let number of blue balls be x.
Red balls are 5.
Total balls = 5 + x
P(E) = (Number of favourable outcomes/ Total number of outcomes)
∴ P (drawing a blue ball) = [x/(x+5)] ——–(i)
P (drawing a red ball) = [5/(x+5)] ——–(i)
From equation (i) and (ii)
x = 10
Hence, the total number of blue balls = 10