Question 327919
let delivering the papers be = 1 job
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girl does it in 45 minutes
1/45 of the job she doe in 1 minute
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together they do the job in 20 minutes
1/20 of the job they do in 1 minute.
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1/20 -1/45 = job done by brother in 1 minute
1/20-1/45=(9-4 )/ 180
=5/180
=1/36 of the job he does in 1 minute
he will take 36 minutes to do the job.