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Sets — Maths STD 11 Science — Question

CBSE BoardEnglish MediumSTD 11 ScienceMathsSets1 Mark
MCQ
If $A = \{2, 3, 4, 5, 7\}, B = \{7, 8, 9\}$, then find $\ce{n(A ∪ B).}$
  • A
    $1$
  • B
    $3$
  • C
    $5$
  • ✓
    $7$
✓

Answer

Correct option: D.
$7$
$A = \{2, 3, 4, 5, 7\}$
$n(A) = 5$
$B =\{7, 8, 9\}$
$n(B) = 3$
$n(A ∩ B) = 1$
$\therefore \ce{(A ∪ B) = n(A) + n(B) − n(A ∩ B)}$
$\ce{(A ∪ B)} = 5 + 3 − 1 = 7$

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