Problem of the Week

The following problem came by way of Herb Bailey, Professor Emeritus at Rose-Hulman Institute of Technology.  

Take a piece of paper and fold it and label it as in the figure above:  

First fold the corner D onto a point D' in the interior of the sheet of paper without moving the corner C.  Next fold the corner C onto the point C' which lies on the interior edge.  

What is the angle PQR?  

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ã2005 Alberto L. Delgado