Question

Let the Universal Set , S, have 132 elements . A and B are subsets of S. Set A contains 63 elements and Set B contains 35 elements . If the total number of elements in either A or B is 89 , how many elements are in A but not in B?

Answer 1

8 elements

Explanation:

From the question given above, the following data were obtained:

Universal set (S) = 132

Set A = 63

Set B = 35

n(AuB)ᶜ = 89

n(A but not in B) =?

Next, we shall determine the number of elements common to both set A and Set B. This can be obtained as follow:

Let the number common to both set A and B be x i.e

(AnB) = x

nA = 63

nB = 35

n(AuB)ᶜ = 89

Universal set (S) = 132

S = nA + nB + n(AuB)ᶜ – (AnB)

132 = 63 + 35 + 89 – x

132 = 187 – x

Collect like terms

132 – 187 = – x

– 55 = – x

Divide both side by –1

x = –55 /–1

x = 55

Thus, the number of elements common to set A and B is 55.

Finally, we shall determine the number of elements in A but not in B as follow:

nA = 63

n(AnB) = 55

n(A but not in B) =?

n(A but not in B) = nA – n(AnB)

n(A but not in B) = 63 – 55

n(A but not in B) = 8

Thus, 8 elements are in set A but not in set B.