A bag contains 4 white balls and some red balls. If the probability of drawing a white ball from the bag is 2/5, find the number of red balls in the bag.

Dear student
solution to your asked query is :

let the number of the red ball be x.
the total number of balls = 6+x.
the probability of drawing a white ball is 2/5.
therefore:
$$\begin{gathered} \frac{6}{6+x}=\frac{2}{5} \\ 2(6+x)=6*5 \\ 6+x=3*5=15 \\ x=15-6 \\ x=9 \end{gathered}$$

thus the number of red balls is 9

Regards

hope this helps you.