question: There are 40 pupils in a class. Half of the class likes blue. One-fourth of the remaining likes green and the rest likes yellow. How many pupils like the color yellow?
answer: There are 40/2 = <<40/2=20>>20 pupils who like blue.
  So, there are now 40 - 20 = <<40-20=20>>20 pupils who like either green or yellow.
  Hence, 20/4 = <<20/4=5>>5 pupils like green.
  Thus, 20 - 5 = <<20-5=15>>15 pupils like yellow.
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