Question

Which of the following pairs is not coprime?
A.4,9
B.5,7
C.9,16
D.9,21

Answer 1

Dear Student,

$$\begin{gathered} \mathrm{D}.9,21\mathrm{is}\mathrm{not}\mathrm{coprime}. \\ \mathrm{As}\mathrm{HCF}\left(9,21\right)=3\ne 1 \\ \mathrm{For}\mathrm{numbers}\mathrm{to}\mathrm{be}\mathrm{coprime}\mathrm{HCF}=1. \end{gathered}$$

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