see question below

Question

gary and his assistant can rake the sand on a beach volleyball court together in 20 minutes. if his assistant could do it alone in 70 minutes, how many minutes would it take for gary to rake the court by himself?

Answer 1

assistant does the job in 70 minutes

assistant does 1/70 of the job in 1 minute

Gary does the job in x minutes

Gary does 1/x of the job in 1 minute

together they do the job in 20 minutes

(1/70)(20)+(1/x)(20)=1  (job finished)

(20/70)+(20/x)=1

(2/7)+(20/x)=1

multiply both sides by 7x

2x+140=7x

140=7x-2x

140=5x

x=140/5

x=28 minutes for Gary to do the job alone