Question 1200463
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Mrs. Brown has 15 children in her first-grade class, and Mr. Lopez has 21 children in his second-grade class. 
The principal has been asked to select 1 student from one of the classes to appear at a PTA meeting. 
How many ways can the selection be made?
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If to follow the text literally as it is written "to select 1 student from one of the classes", 
then there are 15 + 21 = 36 different choices/selections.


If to change the text this way "to select 1 student from each class", 
then there are 15*21 = 315 different choices/selections/pairs.