Question

You can design a web site in 30 hours. Your friend can design the same site in 20 hours. How long will it take to design the web site if you both work together?

Answer 1

12 hrs

Explanation:

Hint:
Use unitary method for better understanding.

Solution:
In 30 hrs, I design 1 site.
So in 1 hr, I design `1/30` part of site.
Similarly in 1 hr, my friend would design `1/20` part of site.
So working together, in 1 hr, we can design `1/30 + 1/20 = (2 + 3)/60 = 5/60 = 1/12` part of site.

Now `1/12` part could be designed in 1 hr.
So 1 site could be designed in `(1)/(1/12) = 12` hrs.