Let the work done per day by
X,
Y and
Z is respectively
x,
y and
z units.
According to the first statement, out of 6 days,
X works for 5 days, and
Y works for 5 days. Total work done
=5x+5y=1 ...(i)
According to the second statement, out of 8 days,
Z works for 7 days and
X works for 6 days and they complete two jobs.
7z+6x=2...
...(ii)
According to the third statement, out of 12 days,
Y works for 10 days and
Z works for 10 days and they complete three jobs.
10y+10z=3 ...(iii)
Solving, we get
x=,y=,z=.
⇒ every day,
X does 10% of the job,
Y does 10% of the job and
Z does 20% of the job.
Together, every day they can do 40% of the job. Hence to complete 100% of the job, they will take
=2.5‌days.