If there are some people, out of which 40% drink coffee, 40% drink tea, 50% drink milk, 10% drink all the three, 20% drink both coffee and tea, 20% drink both tea and milk, 20% drink both milk and coffee?

n(c)=40; n(t)=40; n(m)=40; n(c&t)=20; n(t&m)=20; n(m&c)=20; n(c&t&m)=10 so, n(c or m or t)= n(c)+n(t)+n(m)-n(c&t)-n(c&m)-n(m&t)+n(c&m&t) =40+40+50-20-20-20+10 =80

You can also use Ven diagram for solving this kind of problems. 40%+40%+50%-20%-20%-20%+10% = 80% So, if there is 100 people, 80 of them are drinking any of these.
How could we tell the exact number of people there? If there is 10 people, 4drink tea, 4drink coffee, 5drink milk, 1drinks all the three. 2drink both coffee and tea, 2 drink both tea and milk, 2 drink both milk and coffee... :) so I feel any multiple of 8 could be the answer :D If I'm not wrong, for least case, 8 is the answer ;) (Ans: 8n - where n=1,2,3,...) Please tell whether this helps you or not :)

## Find Number of People

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t=tea

c=coffee

m=milk

n=number of persons

n(c or t or m)=n(c) +n(t) +n(m)-n(c &t)-n(t & m)- n(m & c) +n(c & t & m)

40+40+50-20-20-20+10=80

number of persons=80

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