Problema Solution
One rock crusher can crush the entire load in 4 hours while it takes a second crusher 5 hours to crush the entire load. If both rock crushers are used, how long will it take to crush the entire load.
Answer provided by our tutors
let 'x' be the hours for the both rock crushers to crush the entire load
in 1 hour:
the first rock crusher will crush 1/4 of the load
the second rock crusher will crush 1/5 of the load
together will crush 1/x of the load
1/4 + 1/5 = 1/x multiply both sides by 20x
5x + 4x = 20
9x = 20
x = 20/9
x = 2 2/9 hours = 2 hours 13 min 1/3 sec
the both crushers will do the job in about 2 hours and 13 min.