Question

One person can do a certain job in ten minutes, and another person can do the same job in fifteen minutes. How many minutes will they take to do the job together? 4 min 5 min 6 min

Answer 1

A can do 1 job in 10 min. means 1/10 job per min.
B can do 1/15 job per min.

together A&B can do 1/10+1/15 =1/6 job per min.

1/6 job they spend 1 min
1 spend 1x1/(1/6) = 6 min