Soldier

An experienced soldier digs a good trench in 30 hours. Two soldiers dug the same trench each 40 hours. How many hours will the ditch dig all three together?

Correct answer:

t =  12 h

Step-by-step explanation:

$t={\displaystyle \frac{1}{{\displaystyle \frac{1}{30}}+{\displaystyle \frac{1}{40}}+{\displaystyle \frac{1}{40}}}}=12\text{ h}$

Try another example

Related math problems and questions:

• Flowerbed
  Ondra digs the bed in 20 minutes. Cuba in 30 minutes. For how long do they dig together?
• Garden
  Father dig up the garden in 9 hours. Son in 13 hours. How many hours take dig up the garden together?
• Two diggers
  There are two diggers. One digger digs a pit 46 hours second gidding 2 times faster. a) how long took to dig a pit second digger b) how long took dig together
• Together 3
  If Sally can paint a house in 4 hours, and John can paint the same house in 6 hours, how long will it take for both of them to paint the house together?
• Ditch
  The excavator dug 40% of the excavation in 2 hours 20 minutes. How long does it take him to dig the whole ditch?
• Digging
  The first worker would dig a trench in 6 hours. For the second, the same work would take 4 hours. How long did it take for the trench to be dug if they worked together?
• Two pumps
  The first pump fills the tank in 24 hours second pump in another 40 hours. For how long will it take to fill the tank if it operates both pumps at the same time?
• Madams
  During the spring cleaning ladies going to wash windows. Mother takes wash all the windows 5 hours, the grandmother 3 times longer and Paula wash all windows in 2 hours. How many hours will spend washing the windows this "women's team" if working together
• Workers 2
  Worker dug the trench for 7 hours, another worker for 10 hours. They recruited to work even one worker more. Digging should be done for 2 hours. For how long would dig third worker alone?
• Mow the lawn
  Dano would mow the lawn in 12 hours and Milada in 16 hours. How long will take the lawn mow together?
• Work together
  Two bricklayers plastering a wall. The first would plaster it in 8 hours, the second in 12 hours. How many hours will they be done with the work if they work together?
• Workers
  Two workers will construct the stage at the festival in 54 hours. Organizers need to shorten the assembly time by 42 hours. How many workers must the assembly company send?
• Two rooms
  Woman cleans the room in 30 minutes a man in 90 minutes. How long will take they clean two rooms?
• Machines
  In the workshop are three machines. The first is treated 250 parts for 4.7 hours, the second is treated 300 parts for 1.9 hours, and the third is treated 230 parts for 4.6 hours. How long will it take to make 3100 parts if worked all three machines at the
• Two workers
  One worker needs 40 hours to do a job, and the second would do it in 30 hours. They worked together for several hours, then the second was recalled, and the first completed the job itself in 5 hours. How many hours did they work together, and how much did
• Three pumps
  We are filling the pool. The first pump would be filled in 12 hours, the second pump in 15 hours. If all three pumps were running at the same time, it would fill the pool for 4 hours. How long would the pool fill only with the third pump?
• Oil tank and pipes
  The underground oil tank can be filled by two oil pipelines. The first is filled in 72 hours and the second in 48 hours. How many hours from the moment when first pipeline began to fill the oil is it necessary to start filling it with the second to fill i