First way:  The least common multiple of 12 days and 8 days is 24 days.

>>...A group of 40 workers  can finish digging a tunnel in 12 days...<<

Therefore half as many workers (20 workers) could dig it in twice as many
days (24 days).

Therefore it would take 3 times as many workers (60 workers) to dig it
in one-third of 24 days (8 days).

Answer: 60 workers.


Second way:

Use the job-worker-time formula, which is:



where

W1 = the number of workers in the first situation.
T1 = the number of time units (days in this case) in the first situation.
J1 = the number of jobs in the first situation.

W2 = the number of workers in the second situation.
T2 = the number of time units (days in this case) in the second situation.
J2 = the number of jobs in the second situation.

W1 = 40            W2 = the unknown quantity     
T1 = 12            T2 = 8 
J1 = 1             J2 = 1

[There was only 1 tunnel, so the number of jobs in both situations is 1.





     480 = 8W2
      
Divide both sides by 8

      60 = W2

Answer: 60 workers.

Edwin


 

RELATED QUESTIONS

If a certain job can be finished by 18 workers in 26 days. How many workers are needed to  (answered by robertb)

Six workers can paint 4 houses in 8 days. How many additional workers are needed if the... (answered by edjones)

Six workers can paint 4 houses in 8 days. ahow many additional workers are neededi if the  (answered by ankor@dixie-net.com)

15 workers finish a work in 8 days. How many days would be taken from 12 workers to... (answered by josmiceli,Edwin McCravy)

PLS help me on this word problem.. 18 workers can finish a job in 5 days.how many workers  (answered by nerdybill)

18 workers do a job in 40 days, if 6 workers were added from  the beginning of the job ,... (answered by stanbon)

3 workers can do a job in 36 days. How long would it take 2 workers to finish the same... (answered by macston,Edwin McCravy)

three workers can paint a house in 14 days. assuming that the workers work at the same... (answered by josmiceli)

If a worker can wash all the glass windows of a building in 9 days, what part of the job... (answered by jim_thompson5910)