Solution to puzzle 37

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Let us assume that on that day, Amanda took t minutes to drive half way to her son's school and back home. And as she reached home 40 minutes early, it would have taken t+40 minutes usually.

Let us say Amanda meets her son returning from school at point P. So the travel from P to school and back to P would have caused extra 40 minutes normally.

As she is traveling in a constant speed, the one way journey from point P to Mat's school would take half the time - 20 minutes. 

Amanda would have reached school at 5 pm. Which means she reached point P at 5 pm - 20 minutes = 4:40 pm. So Amanda meets her son at 4:40 pm.

Now Mat has traveled one hour before meeting his mother - so he has started from school at 3:40 pm.  As chess club completes at 5 pm, he has missed 1 hour and 20 minutes of chess practice.

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