Question 1163616
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A survey of 200 college graduates who have been working for at least 3 years found that 
90 owned only mutual funds, 20 owned only stocks, and 70 owned both.
(a) What is the probability that an individual owns a stock? 
(b) A mutual fund?
(c) What is the probability that an individual owns neither stocks nor mutual funds?
(d) What is the probability that an individual owns either a stock or a mutual 
fund?
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Notice that in this problem the mentioned subsets are  DISJOINT.  It is the key to the problem's solution.



<pre>
(a)  P = {{{20/200}}} = {{{1/10}}} = 0.1.


(b)  P = {{{(90+70)/200}}} = {{{160/200}}} = 0.8.


(c)  P = {{{(200-90-20-70)/200}}} = {{{20/200}}} = {{{1/10}}} = 0.1


(d)  P = the complement to the value of (c) = 1 - 0.1 = 0.9.
</pre>

Solved.