Katherine, Amber and Jessica want to assemble a dining room table.

Question

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

Answer 1

Katherine does 1/24 of the job in 1 hour

Amber does 1/12 of the job in 1 hour, or 2/24 of the job

Jessica does 1/8 of the job in 1 hour, or 3/24 of the job

together they do 1/24+2/24+3/24 of the job in 1 hour, or 6/24 of the job which is 1/4 of the job in 1 hour,

2/4 of the job in 2 hours, 3/4 of the job in 3 hours, and the entire job in 4 hours