Question 286877
You need to add their rates of working to get
their rate working together
Let {{{t}}} = their time to finish working together
given:
1st teacher's time is {{{39}}} min
teacher's aide's time is{{{2*39 = 78}}} min
In words:
(1 set of quizzes/teacher's time) + (1 set of quizzes/aide's time) = (1 set of quizzes/time working together)
{{{1/39 + 1/78 = 1/t}}}
multiply both sides by {{{78t}}}
{{{2t + t = 78}}}
{{{3t = 78}}}
{{{t = 26}}}
It will take them {{{26}}} min working together