In how many days will Y alone complete the work? I. X and Y together can complete the wok in 8 days. II. Y and Z together can complete the work in 10 days. III. X and Z together can complete the work in 12 days.

(X + Y)'s 1 day's work = 1/8       ..(i)
(Y + Z)'s 1 day's work = 1/10    ...(ii)
(Z + X)'s 1 day's work = 1/12    ..(iii)
Adding equations i , ii , iii
2(X + Y + Z)'s 1 day's work = 1/8 + 1/10 + 1/12
(X + Y + Z)'s 1 day's work
= 1/2[1/8 + 1/10 + 1/12]    ..(iv)
Subtracting Eq. (iii) from Eq. (iv), we get Y's 1 day's work,
Then, required number of days
= 1/Y's 1 day's work