Question

4.
It takes a lady 3 days to wash the windows
inside and out. Her husband can do the job
in 4 days. How fast can they do it together?

Answer 1

1/tb = 1/t1 + 1/t2
1/tb = 1/3 + 1/4
1/tb = 4/12 + 3/12
7/12 flip reciprocal = 12/7
It takes them 1.71 days