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An algebra class has 21 students who all participate in a welcome activity introducing themselves to each other in pairs. One student wants to know how many introductions were made.Need to find the values of n and r .

Sagot :

Since the total number of students is 21

Since they will work in pairs, that means each group has 2 students

So it is like picking up 2 students from 21 students

That means we will want how many combinations we can do

Then

n = 21

r = 2

We will use the rule of combination

[tex]^nC_r=\frac{n!}{(n-r)!.r!}[/tex]

Substitute the values of n and r in the rule

[tex]\begin{gathered} ^{21}C_2=\frac{21!}{(21-2)!.2!} \\ \\ ^{21}C_2=210 \end{gathered}[/tex]

There are 210 introductions were made