Question

The time taken by artisans A. B and C to do an

embroidery job is 15 hours, 18 hours, and 15 hours.
respectively. A, B, and C begin working together but
after 3 hours B is put on another job. How long will A
and C take to finish the embroidery job?​

Answer 1

3 hours 15mins

Explanation:

in 1 hours time, A will complete 1/15 of the job, B will complete 1/18 and C 1/15.

After 3 hours, A completed 3/15 (aka 1/5) of the job, B 3/18 (aka 1/6) and C being the same as A.

total job done after 3 hrs is 1/5 + 1/6 + 1/5 which is 17/30 of the job

left: 13/30

in 1 hr, A and C will do 2/15 of the job (4/30)

therefore, no. of hours needed: 13/4 hours = 3.25 hours (3 hours 15mins)