Exercise · ZW-ORDER-OF-A-GROUP-005 · ★★☆ Intermediate
What is the order of the group of units mod 15?
Choose one option.
Show answer
- C. 8
Explanation
Count the residues coprime to 15: \(\varphi(15)=\varphi(3)\varphi(5)=2\cdot4=8\). It is not 14, which would be the case of a prime modulus.
Review the concept: Order of a group
The order of a finite group \(G\) is its number of elements; if \(G\) is infinite it has infinite order.
\[|G|\]
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