CBSE Class 11-science Answered
in a town of 10000 families it was found that 40%families buy newspaper a,20% buy newspaper b and 10%buy newspaper c.5% families buy a and b.3% buy b and c and 4% buy a and c.if 2% buy all newspapers.find the number of families that buy
a only
b only
none of a,b and c
Asked by | 25 Feb, 2013, 10:04: AM
n(A) = 40% of 10,000 = 4,000
n(B) = 20% of 10,000 = 2,000
n(C) = 10% of 10,000 = 1,000
n (A
B) = 5% of 10,000 = 500

n (B
C) = 3% of 10,000 = 300

n(C
A) = 4% of 10,000 = 400,

n(A
B
C) = 2% of 10,000 = 200


We want to find n(A only) = n(A) [n(A
B) + n(A
C)] + n(A
B
C)=




n(A only) = 4000 [500 + 400] + 200 = 4000 700 = 3300
Similarly, n(B only) = n(B) [n(A
B) + n(B
C)] + n(A
B
C)




n(B only) = 2000 - [500+300]+200 = 1400
n(none of A, B and C) = 10,000 - [n(A)+n(B) + n(C) - n (A
B) - n(B
C) - n (C
A) + n(A
B
C)]





n(none of A, B and C) = 10,000 - [4000+2000+1000 - 500-300-400 + 200]
n(none of A, B and C) = 4000
Answered by | 25 Feb, 2013, 06:28: PM
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