Question 786860
ONE Job is, "paint the truck".
Ms. Mumford's rate is 1/8 jobs per hour.
Mr. Fisher's rate is 1/10 jobs per hour.
Their combined painting rate is {{{1/8+1/10=(5+4)/40=highlight(9/40)}}} jobs per hour.


The description tells us that HALF the job is needed with Ms. Mumford and Mr. Fisher working together.  We use the uniform rate equation for this type of situation, r*t=j, t is for hours of time and j is for how many jobs.


Use the equation directly:
{{{(9/40)*t=1/2}}}
{{{t=(1/2)(40/9)}}}
{{{highlight(t=20/9)}}} hours, which you can finish in whichever way fits your objective.