Question 1
In how many ways can 8 people be divided into 2 equal teams of 4 each?
Step-by-Step Solution:
Concept: Group division where groups are indistinguishable (no labels like Team A, Team B).
Given:
- Total people: 8
- Group size: 4
- Number of groups: 2
Key Question: Are the groups distinguishable?
- If groups have labels (Team A, Team B): Groups are distinguishable
- If groups have no labels: Groups are indistinguishable (our case)
Strategy for Indistinguishable Groups:
Step 1 - Select first group:
Choose 4 people from 8: C(8,4)
C(8,4) = 8!/[4! × 4!] = 70
Step 2 - Remaining people form second group:
Remaining 4 people automatically form the other group: C(4,4) = 1
Step 3 - Remove overcounting:
Since groups are indistinguishable, we've counted each division twice.
(Selecting ABCD for group 1 and EFGH for group 2 is same as selecting EFGH for group 1 and ABCD for group 2)
Divide by 2! = 2
Calculation:
Total ways = C(8,4) / 2!
= 70 / 2
= 35
General Formula:
For dividing n items into k equal groups of size m each (where n = k×m):
Ways = C(n,m) × C(n-m,m) × ... × C(m,m) / k!
= n! / [(m!)^k × k!]
For our case:
= 8! / [(4!)^2 × 2!]
= 40320 / [24^2 × 2]
= 40320 / [576 × 2]
= 35
Contrast:
- Distinguishable groups (labeled teams): 70 ways
- Indistinguishable groups (unlabeled): 35 ways
Common Error: Forgetting to divide by k! when groups are indistinguishable.
Concept: Group division where groups are indistinguishable (no labels like Team A, Team B).
Given:
- Total people: 8
- Group size: 4
- Number of groups: 2
Key Question: Are the groups distinguishable?
- If groups have labels (Team A, Team B): Groups are distinguishable
- If groups have no labels: Groups are indistinguishable (our case)
Strategy for Indistinguishable Groups:
Step 1 - Select first group:
Choose 4 people from 8: C(8,4)
C(8,4) = 8!/[4! × 4!] = 70
Step 2 - Remaining people form second group:
Remaining 4 people automatically form the other group: C(4,4) = 1
Step 3 - Remove overcounting:
Since groups are indistinguishable, we've counted each division twice.
(Selecting ABCD for group 1 and EFGH for group 2 is same as selecting EFGH for group 1 and ABCD for group 2)
Divide by 2! = 2
Calculation:
Total ways = C(8,4) / 2!
= 70 / 2
= 35
General Formula:
For dividing n items into k equal groups of size m each (where n = k×m):
Ways = C(n,m) × C(n-m,m) × ... × C(m,m) / k!
= n! / [(m!)^k × k!]
For our case:
= 8! / [(4!)^2 × 2!]
= 40320 / [24^2 × 2]
= 40320 / [576 × 2]
= 35
Contrast:
- Distinguishable groups (labeled teams): 70 ways
- Indistinguishable groups (unlabeled): 35 ways
Common Error: Forgetting to divide by k! when groups are indistinguishable.