al can change the oil and rotate a car's tire in 25 minutes. Together Al and Joe can do the same job in 15 minutes. How long would it take for joe to do the job working by himself?

Question

How long would it take for joe to switch the tire on his own

Answer 1

Al’s job rate is 1 job in 25 minutes or 1/25.

Joe’s job rate is 1 job in J minutes or 1/J.

Together their rate is 1/25+1/J=one job in 15 minutes=1/15.

So the equation is 1/25+1/J=1/15.

Multiply through by 75J:

3J+75=5J so 2J=75 and J=37.5 minutes, if Joe did the job on his own.