Question 258979
This is a working together or job / time problem. We use the following formula
(J1/T1)(x) + (J2/T2)(x) = TJ
where
J1 = person 1's job
T1 = person 1's time
J2 = person 2's job
T2 = person 2's time
x = time together
TJ = total number of jobs
--
From the given information we get
{{{(1/3)(x) + (1/4)(x) = 1}}}
-- 
step 1 - multiply by 12 to get
{{{4x + 3x = 12}}}
step 2 combine like terms to get
{{{7x = 12}}}
step 3 - divide to get
{{{x = 12/7}}}
So it will take them together 12/7 hrs or ~ 1.71 hours