Question 151997
We respect everybody here, but there's no harm in trying this one:
Total years working= {{{20}}} years
1st year earnings: $20,000
2nd year: $20,500..... adding $500 after the 1st year
So we can arrive to an eqn:
{{{(20000*20years)+((n-1)(500))}}} ------> total salary
where {{{n}}}= no. of years. Why there's (-1) in the eqn? Because the increased started on the 2nd year. Continuing,
{{{(400000)+((20-1)(500))}}}
{{{400000+9500}}} 
$409,500 ------------------------> Total salary.
For Mean Salary:
{{{409500/20}}}= $20,475 --------> Mean salary
Thank you,
Jojo