Problema Solution
the county's new asphalt paving machine can surface 1 km of highway in 10 h. A much older machine can surface 1km in 18h. how long will it take them to surface 21 km of highway if they start at opposite ends and work day and night?
Answer provided by our tutors
We have two machines, old and the new one, for both of them to complete 21kms we start with the combined rate of the 2 per hour.
So we have,
old asphalt paving machine rate is 1km/10hrs = 0.1km/hr
new asphalt paving machine rate is 1km/18hrs = 0.0555556 km/hr
Together their rate is 0.1555556 km/hr
So, for 21Kms time taken = 21/0.1555556 = 135 hours