Question 495031
13 through 37 is the same as
{{{ 12*25 = 300 }}} ( there are 25 numbers to add )
add to this the numbers 1 through 25
The formula for this is:
{{{ (1/2)*25*26 = 325}}}
{{{ 300 + 325 = 625 }}} 
The average is:
{{{ 625/25 = 25 }}} answer
Hope I got it