At least 1 intern is arranged for each position.
The number of people in the three positions is 2-2- 1 or 3- 1- 1.
1) 2-2- 1
Select 1 post, and assign a person C (31) C (51) =15.
There are two people in the other two positions. C(4，2)C(2，2)=6。
Multiplication principle: 15×6=90.
2)3- 1- 1 distribution
Select 1 post, and assign 3 people. C(3,1) C (5,3) = 30.
The other two posts have 1 person. A(2，2)=2。
Multiplication principle: 30*2=60
Total: 90+60= 150
There are 150 different distribution methods.