Question 365424
Martha can rake the leaves in her yard in 4 hours.
So she does 1/4 of the job in 1 hour
 Her younger brother can do the job in 6 hours.
so he can do 1/6 of the job in 1 hour
Together they will do 1/6 +1/4 of the job in 1 hour
= (2+3)/12 
=5/12
They do 5/12 of the job in 1 hour
so they will do the job yogether in 12/5 hours
=2.4 hours
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m.ananth@hotmail.ca