For example, a coin has two possible outcomes: heads or tails.
Probability of heads is 1/2 and probability of tails is 1/2 for one toss. 1/2+1/2=1.
Another example: consider six-headed die where each face has a probability of 1/6 for a single toss. But all the outcomes is added to 1 since its sum is 6*(1/6)=1.
I hope the above steps were helpful.
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