Question 1198441
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Step 1:  You select 3 men from 20 men to the 1st section in  {{{C[20]^3}}} = 1140 different ways.
Step 2:  Next, you select 5 men from the remaining 20-3 = 17 men in  {{{C[17]^5}}} = 6188 different ways.

Step 3:  After that, you do not need to select the men into the third section: the rest of the men 
         after steps 1 and 2 just form this third section.



Step 4: To find the total number of ways, multiply the numbers from steps 1 and 2.



Doing this way, you will obtain the answer.
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Solved in simple steps, with explanations.