Question 198741
let x="time to fill pool" (in hours)


in x hours, the 8 hour pipe fills x/8 of the pool


in x hours, the 12 hour pipe fills x/12 of the pool


in x hours, the 15 hour drain empties x/15 of the pool


the fractions total to 1, one full pool


x/8 + x/12 - x/15 = 1


multiplying by 120 (LCD) ___ 15x + 10x - 8x = 120


17x = 120 ___ x = 120/17 ___ x = 7.06 (approx)