A bag contains 5 black, 4 white and x red marbles. If the probability of picking a red marble is 2/5, find the value of x
A
8
B
10
C
4
D
6
Verified Correct Answer: D.
Step-by-Step Mathematical Solution
Black = 5
White = 4
Red = x
Total = 9+x
P(red) = 2/5
x / (9+x) = 2/5
5x = 2(9+x)
5x = 18+2x
5x-2 = 18
3x = 18
x = 6
Source: Myschool Past Questions Archive (Record #8656)