question: A singer has 50 microphones that he wants to arrange in pairs on a stage. While making the arrangement, he realizes that 20% of the microphones won't find any space to fit in after arranging the rest in pairs. How many pairs of microphones was he able to arrange on the stage?
answer: The number of microphones that were not able to find space on the stage is 20/100*50 = <<20/100*50=10>>10
  This means the singer could set 50-10 = <<50-10=40>>40 microphones into pairs on the stage.
  Since a pair has 2 microphones, the singer set up 40/2 = <<40/2=20>>20 pairs of microphones on the stage.
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