Question 211416
Let A = time it takes Anthony to do the job alone
D= time for Donita to do the job alone = 14 hours
T= time for Anthony and Donita to do the job together= 21/5 hours
    

The basic equation is {{{1/A + 1/D = 1/T}}}
{{{1/A + 1/14=1/(21/5)}}}
{{{1/A + 1/14 = 5/21}}}


The LCD for the equation is actually 7*2*3*A = 42A, so multiply both sides of the equation by 42A.


{{{42A*(1/A)+ 42A*(1/14) = 42A*(5/21) }}}

{{{42 + 3A = 10A }}}
{{{42 = 7A }}}
{{{6 = A}}}


Anthony will take 6 hours to complete the project alone.


R^2


Dr. Robert J. Rapalje, Retired