Monday, March 4, 2013

The Earned Run Average (ERA).

Question:  What is an Earned Run Average (ERA)?  One pitcher gave up 12 earned runs in 49  innings pitched.  A second pitcher gave up 16 earned runs in 57 innings pitched.  What are the ERAs for the two pitchers?

Answer:  The Earned Run Average is the average  number of earned runs given up per 9 inning pitched.  The formula for the earned run average is

ERA = (ER/(IP/9))


ERA is the earned run average,
ER is the number of earned runs,
IP is innings pitched,
IP/9 is the  number of 9-innning intervals.

Note that the ERA can be rewritten as


Plugging numbers into either equation we obtain:

ERA for pitcher one:

ERA_P1= 9x12/49 = 2.20

ERA_P2= 9x16/57 = 2.53

Note:  I am still thinking about posting tips on associative and commutative properties.  When I think this through I will post the material on

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