In a group of 100 persons, 85 had Rh positive blood (Rh factor present), 45 had Type O blood, and 38 had both type O and Rh positive blood. If one person had been selected at random from the group, what would the probability be:
that his blood type was Type O and Rh+?
that his blood type was not O?
that his blood type was Rh-?
that his blood type was Type O and Rh-?
that his blood type was Rh+?
that his blood type was not Type O or else was Rh+?

Question

In a group of 100 persons, 85 had Rh positive blood (Rh factor present), 45 had Type O blood, and 38 had both type O and Rh positive blood. If one person had been selected at random from the group, what would the probability be:
that his blood type was Type O and Rh+?
that his blood type was not O?
that his blood type was Rh-?
that his blood type was Type O and Rh-?
that his blood type was Rh+?
that his blood type was not Type O or else was Rh+?

amistre64 · Answer

something to do with:  P(A) + P(B) - P(AnB) seems familiar

amistre64 · Answer

P(AuB) = ....  when A and B are not independant

amistre64 · Answer

or the more brute method is to venn it up

amistre64 · Answer

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amistre64 · Answer

since it asks for probability, you would need to convert those %s to decimals

anonymous · Answer

Sorry, I was away from the computer. & I'm not really sure how to do that? I just don't understand how it adds up to 100 because its 85, 45, and 38 and that isn't even

amistre64 · Answer

notice that the intersection, people with BOTH O and Rh is 38

this contributes to both groups of O and Rh

x + 38 = 85
y + 38 = 45

amistre64 · Answer

x = 47, y = 7   are the areas of the corresponding venn diagram

amistre64 · Answer

since 7+47+38 = 92, that leaves 8 left over that are neither

amistre64 · Answer

if we simply make the mistake and add up 85 and 45

x + 38 = 85
y + 38 = 45

x + 38 + y + 38 ... we have counted the "38"  twice, 
                            so we need to subtract out a 38

   85    +    45     -    38   is the total of the sets ....

anonymous · Answer

Oh, okay. I see that now. So when I'm trying to find the fractions do I use the numbers they gave me or the ones that you have found out?

amistre64 · Answer

id use the numbers i found out,  do you have to make fractions?  the decimals are simple enough

anonymous · Answer

Yes I have to use fractions.. So for like
that his blood type was Type O and Rh+?
what would I do?

amistre64 · Answer

|dw:1368030232046:dw|

amistre64 · Answer

O and Rh was already given in the setup ....   it is also located at the intersection of the 2 circles:  .38

amistre64 · Answer

notO  is all the values that are NOT in O:  .47 + .08

amistre64 · Answer

that his blood type was Rh-?  are all the values that are NOT in Rh:  .07+.08

anonymous · Answer

Oh okay, so it's not super complicated, its really just adding the proper numbers?

amistre64 · Answer

correct

blood type was Type O and Rh- ?  everyting in O that is NOT in Rh: .07

anonymous · Answer

Oh okay, I see now. Well thank you so much for your help :)

amistre64 · Answer

good luck ;)

anonymous · Answer

I just checked my answers & I got them all right! I started out using decimals and then converted them to fractions. It was way easier that way. Thanks again!