Exercise · ZW-LAGRANGES-THEOREM-002 · ★☆☆ Basic
A group of order \(15\) has a subgroup \(H\) of order \(5\). What is the index \([G:H]\)?
Choose one option.
Show answer
- A. \(3\)
Explanation
By Lagrange, \([G:H]=|G|/|H|=15/5=3\). The product \(75\) comes from multiplying instead of dividing.
Review the concept: Lagrange's theorem
If \(H\) is a subgroup of a finite group \(G\), the order of \(H\) divides the order of \(G\), and the quotient is the index \([G:H]\).
\[|G|=[G:H]\,|H|\]
More practice problems: lagrange's theorem
- ZW-LAGRANGES-THEOREM-001 A group G has order 20. Which of these can NOT be the order of a subgroup of G?
- ZW-LAGRANGES-THEOREM-003 How many subgroups does a group of order 11 have?
- ZW-LAGRANGES-THEOREM-004 The group S_4 has order 24. Which statement is correct?
- ZW-LAGRANGES-THEOREM-005 A group of order 36 has a subgroup of index 4. How many elements does that subgroup have?
- ZW-LAGRANGES-THEOREM-006 A group of order 48 has a subgroup of order 6. What is its index?
- ZW-LAGRANGES-THEOREM-007 A_4 has order 12. Which statement about its subgroups is true?
- ZW-LAGRANGES-THEOREM-008 Two subgroups H and K of a group have orders 12 and 18. Which can NOT be |H∩ K|?
- ZW-LAGRANGES-THEOREM-009 Let |G|=48 and H a subgroup of order 8. If K is a subgroup with Hsubsetneq Ksubsetneq G, which can…