Question Part Points Submissions Used In a group of 130 stud

Question Part Points Submissions Used In a group of 130 students, 75 use craigslist, 65 use eBay, and 30 use neither. (a) How many students know how to use both websites?

Solution

Total number of students are 130; out of which the students that use neither are 30;

Hence the total number of students who use at least one website is = 100;
n(C) = number of users of Craigslist=75
n(E)= number of users of eBay=65
n(C U E) = number of users of at least 1 of the two websites; which in this case = 100;

hence n(C U E)= n(C)+n(E)- number of stuednts who know how to use both wesbites ( say \"X\"); also known as n(C intersection E) ;

Substituting the values given in the question in the above equation

100=75+65-X;

X= 140-100=40;

Thus a total of 40 students know how to use both the websites;