Hi, 

One robot can vacuum a house in 10 hours. If a second robot is added and both

 are used, the same job can be completed in 3 hours

Let x represent the time the second robot would take alone:

PER hour KEY:

 1/10 + 1/x = 1/3 ||Multiplying thru by 30x so as all denominators = 1

 3x + 30 = 10x

     30 = 7x

     4 2/7 hr = x, the time the second robot would take alone 

RELATED QUESTIONS

An elf in Santa’s Workshop can typically build two giant robot toys a week. If the elf... (answered by stanbon)

Chris can construct a robot on an erector set in 7 hours.  His friend, Cristobal, can... (answered by stanbon)

Robot A takes 6 minutes to weld a frame.  With the help of Robot B, the job can be done... (answered by Edwin McCravy)

Ship-Cleaning Robots
When a ship arrives in port, an underwater robot cleans the outside  (answered by CPhill)

In the same amount of time a new production assembly robot can assemble 8 times as many... (answered by scott8148)

8. An elf in Santa’s Workshop can typically build two giant robot toys a week. If the elf  (answered by josgarithmetic)

In the same amount of time a new production assembly robot can assemble 8 times as many... (answered by josmiceli)

A space station has 3 robots that make repairs.
The Marp robot can make 12 repairs in 10  (answered by macston)

one drain pipe can empty a swimming in 6 hr. Another pipe takes 3 h. if both are used at... (answered by mananth,richwmiller)