it take Katherine 24 hrs, Amber 12 hrs and Jess 8 hrs to assemble it by themselves. How long would it take all three girls to assemble it if they work together?

Question

This is from Pre-cal 126 college course. Not understanding how to work these problems

Katherine, Amber and Jess want to assemble a dining table. Individually it would take Katherine 24 hrs, Amber 12 hrs and Jess 8 hrs to assemble it by themselves. How long would it take all three girls to assemble it if they work together?

Answer 1

Jess = 8/8 = 1     Amber = 8/12 = 2/3       Katherine = 8/24 = 1/3

 

first hour 1 + 2/3 + + 1/3 = 2 hours work done

 

8 hours / 2 hours = 4 hours for all three girls to assemble the dining room table.