A ball is selected at random from a box holding 6 red,5 white and 4 black balls.what is the probability that the ball is red or black?

To find the probability that the ball is red or black, we need to calculate the total number of red and black balls and divide it by the total number of balls in the box.

Total number of red balls = 6
Total number of black balls = 4

Total number of red or black balls = 6 + 4 = 10

Total number of balls in the box = 6 + 5 + 4 = 15

Therefore, the probability that the ball is red or black is:

P(red or black) = (Number of red or black balls) / (Total number of balls)
P(red or black) = 10 / 15
P(red or black) = 2 / 3

So, the probability that the ball is red or black is 2/3 or approximately 0.67.

Total number of balls = 6 + 5 + 4 = 15

Number of red balls = 6

Number of black balls = 4

Probability of selecting a red or a black ball = (Number of red balls + Number of black balls) / Total number of balls

= (6 + 4) / 15

= 10 / 15

= 2 / 3