Answer:
4.8 hr, or 4 hr 48 min
Step-by-step explanation:
Let '1' represent 'the whole house-painting job.'
Then perform a dimensional analysis:
1 whole house job
-------------------------------- = 12 hours. →This restates the obvious: Jim can
1 job/ 12 hrs paint a house in 12 hours.
Now if both people work together, the total time required to paint the house is:
1 house job 1 house job
----------------------------------------- = ------------------------------ = t for whole job
1 job 1 job 8 job-hr + 12 job-hr with both people
------------ + ------------ ----------------------------- working
12 hours 8 hours 96 hr
This turns out to be:
1
-------------------------- = 96/20 hr = 4.8 hr, or 4 hr 48 min
20/96