Question 876178
Starting with the one-man rate would be most comfortable.


One man works at the rate of {{{1/(40*60)}}} walls/day.  In a simple way, setup some terms to start building an equation equaling to one wall.


{{{60(1/2400)*10+55(1/2400)10+50(1/2400)10+MoreTerms=1}}}
{{{1/4+55/240+5/24+45(1/2400)10+MoreTerms=1}}}
{{{1/4+11/48+5/24+45/240+MoreTerms=1}}}
{{{1/4+11/48+5/24+9/48+MoreTerms=1}}}

{{{1/4+11/48+5/24+9/48+40(1/2400)10+MoreTerms>1}}}-----Forty days
{{{1/4+11/48+5/24+9/48+1/6=1.041&2/3}}}-------Forty days


What you can do with this is use the forty-day equation, and add a term in which the time quantity is a variable, to be solved.  This term is {{{40(1/2400)d}}}, and make the equation equal to 1.


{{{1/4+11/48+5/24+9/48+40(1/2400)d=1}}}
{{{highlight(1/4+11/48+5/24+9/48+(1/60)d=1)}}}, solve for d.