# Can't understand question

In C3_W2_Assignment, Exercise 3, what does the question ask exactly? Whats meant by “P for sum=2|8”. I don’t understand what meant by 2|8, do they mean to ask “P for sum=2”? or “P for sum=8”?

@Musab_Bin_Gulfam I am not familiar with this particular exercise, but in probability/statistics ‘|’ (the pipe symbol) typically means ‘given’.

In which case ‘P for sum=2|8’ would be read as: ‘What is the probability our sum is 2, given our variable in question has a value of 8 ?’

(*and of course your probability, P, will always be some value between zero and one, inclusive)

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Thank you @Nevermind for your explanation.

Just to add a few things.

Unfortunately, without further context, the exact meaning of “P for sum=28” remains ambiguous. However, this could represent a conditional probability, where we are interested in the probability of getting a sum of 2 given that we know one of the values is 8. In this case, the notation is read as “the probability of the sum being 2, given 8”.

For your information, Conditional probability is a way to figure out how likely something is to happen if another thing has already happened.

Think about taking rocks out of a bag. If you already know that a blue marble was drawn first and then taken away, the chance of drawing a red marble changes. This is because the first event (drawing blue) changes the way the second event (drawing red) can happen.

Bag with 3 blue marbles and 5 red marbles:
P(Red): 5/8 (chances of getting red on the first draw)
P(Red|Blue): 5/7 (probability of red after a blue was removed)

I hope this will help you to understand the concept of Conditional Probability @Musab_Bin_Gulfam

This is a mis-use of a notation that’s normally used for a different purpose.

In the context of this assignment, P(2|8) means “What is the probability that the sum = 2 given that the maximum possible sum is 8?”

I’ll submit a support ticket to ask course staff to fix this.

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