MathCastle
Groups and FieldsMediumGroups and the Group Axioms

Groups and the Group Axioms · Medium problem

In (Z10,×)(\mathbb Z_{10},\times), cancellation can fail. For x=3x=3, how many values y∈{0,1,…,9}y\in\{0,1,\ldots,9\} with y≠3y\ne3 satisfy 2y≡2×3(mod10)2y\equiv2\times3\pmod{10}?