Misc 16 - Chapter 1 Class 11 Sets

Transcript

Misc 16, In a survey it was found that 21 people liked product A, 26 liked product B and 29 liked product C. If 14 people liked products A and B, 12 people liked products C and A, 14 people liked products B and C and 8 liked all the three products. Find how many liked product C only. Let A, B, C be the set of people who like product A, product B & product C respectively Number of people who liked product A = n(A)= 21, Number of people who liked product B = n(B)= 26, Number of people who liked product C = n(C) = 29, Number of people who liked product A and B = n(A B) = 14, Number of people who liked product C and A = n(C A) = 12, Number of people who liked product B and C = n(B C) = 14, Number of people who liked all three products A ,B and C = n(A B C) = 8 We have to find how many people liked product C only. Let us draw a Venn diagram Let a denote the number of people who liked product A & B but not C. Let b denote the number of people who liked product A & B but not C. Let c denote the number of people who who liked product A & B but not C. Let d denote the number of people who liked all three products. Number of people who liked product C only = n(C) b d c Now, d = n(A B C) = 8 Given n(A C) = 12 b + d = 12 Putting d = 8 b + 8 = 12 b = 12 8 = 4 Similarly, n(B C) = 14 c + d = 14 Putting d = 8 c + 8 = 14 c = 14 8 = 6 Number of people who liked product C only = n(C) b d c = 29 4 8 6 = 11 Hence, number of people who like product C only is 11