Question

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 .

Answer 1

here you go

Explanation:

plato

Answer 2

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

`^nC_r=(n!)/((n-r)!.r!)`

Substitute the values of n and r in the rule

`\begin{gathered} ^(21)C_2=(21!)/((21-2)!.2!) \\ \\ ^(21)C_2=210 \end{gathered}`

There are 210 introductions were made