SOLUTION: In a group of 40 students, 20 have cats, 15 have dogs, and 4 have both cats and dogs. (a) How many students have neither cats nor dogs? (b) How many students have cats but not

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Question 254151: In a group of 40 students, 20 have cats, 15 have dogs, and 4 have both cats and dogs.
(a) How many students have neither cats nor dogs?
(b) How many students have cats but not dogs?

Found 2 solutions by dabanfield, solver91311:
Answer by dabanfield(803)   (Show Source): You can put this solution on YOUR website!
In a group of 40 students, 20 have cats, 15 have dogs, and 4 have both cats and dogs.
(a) How many students have neither cats nor dogs?
(b) How many students have cats but not dogs?

Of the 20 people who have cats, 4 also have dogs so 20-4 = 16 have cats only. Similarly 15-4 = 11 have dogs only. So we have:
16 cats only
11 dogs only
4 both dogs and cats.
The remaining students, 40-(16+11+4) = 9, have neither dogs nor cats.

Answer by solver91311(24713)   (Show Source): You can put this solution on YOUR website!


If 4 have both cats and dogs and 20 have cats, then 16 must have a cat but not a dog. Similarly, if 4 have both and 15 have dogs, then 11 must have dogs but no cats.

So 16 plus 4 plus 11 equals 31 of the 40 students have one or the other or both leaving 9 that have neither.


John


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