**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))

where

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

ERA = 9xER/IP

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 www.factiontips.blogspot.com

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