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# Cumulative geometric probability (less than a value)

AP.STATS:
UNC‑3 (EU)
,
UNC‑3.E (LO)
,
UNC‑3.E.2 (EK)
Probability for a geometric random variable being less than a certain value.

## Want to join the conversation?

• Why we are not considering P(C = 0)?
• Think about it. P(C = 0) is actually 0, since C = 0 means 0 cake order, right? Without a cake order, there is 0% probability of receiving an order over the telephone. You could include it, if you want to, but it just evaluates to 0, so we don't include it.
• Is that right?
The way I understand is: what's the probability that she receives at least 1 telephone order in the 1st 4 orders. The complement of which is no telephone orders in the 1st 4 orders, so 1 - p(no telephone order)
• She's receiving orders until she gets the first telephone one. So it is not about at least 1.
• Hi, it seems to me that here we are calculating the probability that C = 4. Is that really the same as calculating the probability that C<5?

If our condition is C<5, then C could take on 1,2,3 or 4, all in equal probabilities I assume. Are we taking that into account?