Question

using the definition of a probability, explain in your own words why the probability of an event that must occur is 1.

Answer 1

Definition of Probability: A measure of how likely it is that an event will occur.

Can you now explain why the probability of an event that must occur is 1, keeping in mind that the maximum value of the probabilty of an event occuring is 1.

Answer 2

To me, probability is synonymous with likelihood:

Consider a coin:

If you flip a coin, the likelihood (probability) of landing on heads is .5

That means there is a 50% chance that the coin will land on heads. You see, probability is given as a decimal.

Similarly, for the same coin, the likelihood (probability) of landing on tails is also .5

That means that there is a 50% chance that the coin will land on tails.

The probability of an EVENT (either heads or tails) is .5 + .5 = 1

Answer 3

I left out a few technical details (like 50% chance occurring as the number of trials gets very large). I hope you get the idea.