I need help on probability!! The question is The probability that you will get grounded if you have a bad grade is 85%. The probability that you will get grounded and have extra chores is 50%. What is the probability that you will have extra chores given that you are already grounded?

Question

anonymous · Answer

@amistre64 can you help me?

anonymous · Answer

the probability when you get bad grades that you will get grounded and have extra chores is 50%?

anonymous · Answer

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anonymous · Answer

do you understand this schematic?

anonymous · Answer

yes

anonymous · Answer

ok, then all you need to do is solve for the appropriate question mark and you'll have the answer. Let me know if you have any other questions.

anonymous · Answer

@zimmah I am still pretty confused

anonymous · Answer

ok, what part confuses you?

anonymous · Answer

all of it

anonymous · Answer

ok

anonymous · Answer

well, with probability, the sum of all the chances always is 1 (100%) so. We know there is a 85% chance of being grounded, and a 15% chance of not being grounded.

On top of that, we know there is a 50% chance of getting grounded and having extra chores and therefore also a 35% chance of getting grounded but not having extra chores.

anonymous · Answer

Since we want to know what chance we have of getting extra chores after being grounded, we need to calculate that from the total chance of getting chores (0.5) divided by the chance of being grounded (0.85) 

because 0.85 * x = 0.5 so x = 0.5/0.85

anonymous · Answer

you will see that this will add up because if you do the same for 0.35/0.85 it will all add up to 1 again

anonymous · Answer

but 0.5/0.85 will be the answer you seek.

anonymous · Answer

okay i got .58

anonymous · Answer

yes, so about 58% chance

anonymous · Answer

okay thank you. I'll probably have another one so can I ask you if I do?

anonymous · Answer

sure

anonymous · Answer

Okay heres my next one: The probability of rain and hail during a storm is 16%. The probability of only rain is 78%. What is the probability of hail given that there is already rain?

anonymous · Answer

ok, let me make a schematic of that as well

anonymous · Answer

hmm, let me think, this one is a little different in approach

anonymous · Answer

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anonymous · Answer

i think this should be it

anonymous · Answer

so x=17% and y=82%