Question 131398
Let t be the time it takes them working together
Father does 1/3 of the job in 1 hr.
Son does 1/4 of the job in 1 hr.
Together they do 1/t of the job in 1 hr.
1/3 + 1/4 = 1/t
4t+3t=12 multiply each side by 12t to eliminate fractions.
7t=12
t=12/7 hrs or 1 hr 43 min (approx.)
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Ed