6.Permutation and Combination
hard

माना $\mathrm{S}=\{1,2,3,5,7,10,11\}$ है। $\mathrm{S}$ के अरिक्त उपसमुच्चयों, जिनके सभी अवयवों का योग $3$ का एक गुणज है, की संख्या है__________. 

A

$42$

B

$43$

C

$41$

D

$40$

(JEE MAIN-2023)

Solution

Elements of the type $3 k =3$

Elements of the type $3 k +1=1,7,9$

Elements of the type $3 k +2=2,5,11$

Subsets containing one element $S_1=1$

Subsets containing two elements

$S_2={ }^3 C_1 \times{ }^3 C_1=9$

Subsets containing three elements

$S_3={ }^3 C_1 \times{ }^3 C_1+1+1=11$

Subsets containing four elements

$S_4={ }^3 C_3+{ }^3 C_3+{ }^3 C_2 \times{ }^3 C_2=11$

Subsets containing five elements

$S_5={ }^3 C_2 \times{ }^3 C_2 \times 1=9$

Subsets containing six elements $S_6=1$

Subsets containing seven elements $S_7=1$

$\Rightarrow \text { sum }=43$

Standard 11
Mathematics

Similar Questions

Start a Free Trial Now

Confusing about what to choose? Our team will schedule a demo shortly.