ANSWER:
165 different groups
STEP-BY-STEP EXPLANATION:
Since either person can answer any phone, no matter what order, we use the following combination formula:
[tex]_nC_r=\frac{n!}{r!(n-r)!}[/tex]
In this case, n is equal to 11 and r = 3, therefore:
[tex]\begin{gathered} _{11}C_3=\frac{11!}{3!(11-3)!}=\frac{11!}{3!\cdot8!} \\ \\ _{11}C_3=165 \end{gathered}[/tex]
This means that 165 different groups of three people can answer these lines
