Probability of Household Pet Ownership

In a recent survey of 100 households in a city, it was found that 30 households owned a dog, 20 households owned a cat, and 10 households owned both a dog and a cat. Based on this data, calculate the probability that a randomly selected household either owns a dog or a cat.

Use the principle of inclusion-exclusion for your calculation. Let D be the event that a household owns a dog, and C be the event that a household owns a cat.