The probability that all 4 co-captains come from the same class is 0.0442
The probability of coming from the same class can be defined thus :
They can either be Juniors , Seniors or Sophomores
Total number of students = (11 + 13 + 5) = 29
All juniors :
- 11/29 * 10/28 * 9/27 * 8/26 = 0.0139
All Seniors :
- 13/29 * 12/28 * 11/27 * 10/26 = 0.0301
All Sophomores :
- 5/29 * 4/28 * 3/27 * 2/26 = 0.000211
P(All come from the same class) = 0.0139 + 0.0301 + 0.000211 = 0.0442
Hence, the probability that all 4 co-captains come from the same class is 0.0442