Answer:
3 : 7
Step-by-step explanation:
If the probability of choosing red = 3/10
The we can infer that ; ratio of the number of red marbles to the total number of marbles = 3 : 10
Thus number if marbles that aren't red :
10 - 3 = 7
The odd in favor of picking a red marble :
Red : not red
3 : 7
