SOLUTION: most tunnels are drilled using tunnel-boring machines that begin at both ends of the tunnel. suppose a new tunnel is being built and one tunnel-boring machine alone can finish the

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Question 963673: most tunnels are drilled using tunnel-boring machines that begin at both ends of the tunnel. suppose a new tunnel is being built and one tunnel-boring machine alone can finish the tunnel in 4 years. a different type of machine can tunnel to the other side in 3 years if both machines start at a opposite ends and work at the same time, when will the tunnel be finished?
Answer by ankor@dixie-net.com(22740) (Show Source):
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most tunnels are drilled using tunnel-boring machines that begin at both ends of the tunnel. suppose a new tunnel is being built and one tunnel-boring machine alone can finish the tunnel in 4 years.
a different type of machine can tunnel to the other side in 3 years if both machines start at a opposite ends and work at the same time, when will the tunnel be finished?
:
let t = time required when both drills are used
let the completed job = 1
:
Each machine will do a fraction of the job, the two fractions add up to 1
+ = 1
multiply equation by 12, cancel the denominators, you have:
3t + 4t = 12
7t = 12
t = 12/7
t = 1.714 years or 1 + .714(365) = 1 yr 261 days to finish the tunnel