<p>Why does the select statement below return two different values ?</p>

<pre><code>declare @tempDec decimal
set @tempDec = 1.0 / (1.0 + 1.0)
select @tempDec, 1.0 / (1.0 + 1.0)
</code></pre>

I found out from a coworker just as I posted this.
You need to specify the default precision and scale.
This works in this scenario:
declare @tempDec decimal(3,2)
From MSDN:
decimal[ (p[ , s] )] and numeric[ (p[ , s] )] 
Fixed precision and scale numbers. When maximum precision is used, valid values are from - 10^38 +1 through 10^38 - 1. The SQL-92 synonyms for decimal are dec and dec(p, s). numeric is functionally equivalent to decimal.
p (precision) 
The maximum total number of decimal digits that can be stored, both to the left and to the right of the decimal point. The precision must be a value from 1 through the maximum precision of 38. The default precision is 18.
s (scale) 
The maximum number of decimal digits that can be stored to the right of the decimal point. Scale must be a value from 0 through p. Scale can be specified only if precision is specified. The default scale is 0; therefore, 0 <= s <= p. Maximum storage sizes vary, based on the precision.