On occasion of Deepawali festival each student of a class sends greeting cards to others. If there a

English

Gujarati

Hindi

6.Permutation and Combination

easy

On the occasion of Deepawali festival each student of a class sends greeting cards to the others. If there are $20$ students in the class, then the total number of greeting cards exchanged by the students is

A

$^{20}{C_2}$

B

$2\;.{\;^{20}}{C_2}$

C

$2\;.{\;^{20}}{P_2}$

D

None of these

Solution

(b) $2\;.{\;^{20}}{C_2}$ {Since two students can exchange cards each other in two ways}.

Standard 11

Mathematics

Share

Similar Questions

If $a, b$ and $c$ are the greatest value of $^{19} \mathrm{C}_{\mathrm{p}},^{20} \mathrm{C}_{\mathrm{q}}$ and $^{21 }\mathrm{C}_{\mathrm{r}}$ respectively, then

hard

(JEE MAIN-2020)

For a scholarship, atmost $n$ candidates out of $2n+1$ can be selected. If the number of different ways of selection of atleast one candidate for scholarship is $63$, then maximum number of candidates that can be selected for the scholarship is –

normal

How many numbers greater than $1000000$ can be formed by using the digits $1,2,0,2,4,2,4 ?$

medium

The number of words (with or without meaning) that can be formed from all the letters of the word $"LETTER"$ in which vowels never come together is

medium

(JEE MAIN-2020)

What is the number of ways of choosing $4$ cards from a pack of $52$ playing cards? In how many of these

four cards are of the same suit,

medium