Final answer:
The number of red balls in the box is 30.
Step-by-step explanation:
To find the number of red balls, we can set up the equation:
Probability of drawing a red ball = Number of red balls / Total number of balls
Given that the probability is 0.3 and the total number of balls is 100, we can solve for the number of red balls:
0.3 = r / 100
r = 0.3 * 100
r = 30
Therefore, there are 30 red balls in the box.