Question 613378
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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