Question

if (A) = 15 , n(AuB) = 29 , n(AnB) = 7 find n (B).

Answer 1

$\fbox{\bold {ANSWER}}$

n( A⋃ B) = n ( A) + n ( B ) - n ( A ⋂ B)

29 = 15 + n ( B ) - 7

29 = 8 + n ( B )

n ( B ) = 29 - 8

n ( B ) = 21.

Answer 2

Hey mate
there are two ways to find this ans
1.my formula
2.by venn diagram


the formula to find this is:
(aub) =n(a)+n(b)-n(anb)
so u can substitute the info and u will get
29=15+x-7
so n(b)=21
i hope u understood!!!