Question 969329
The sequence is:
23, 26, 29, 32, . . . for 38 rows
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This is  {{{ 20*38 = 760 }}}  plus the sequence:
3, 6, 9, 12, . . .  for 38 rows
This is:
{{{ 3n }}}  where {{{ n }}} is the row number , and
summed over the 38 rows
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This is {{{ 3 }}} times
{{{ n }}} row numbers summed over the 38 rows
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The formula for the summation is:
{{{ ( n*( n+1 ) ) / 2 = ( 38*39 ) / 2 }}}
{{{ ( n*( n+1 ) ) / 2 = 1482 / 2 }}}
{{{ ( n*( n+1 ) ) / 2 = 741 }}}
{{{ 3*741 = 2223 }}}
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{{{ 760 + 2223 = 2983 }}}
There are 2,983 seats in the theater
hope I got it