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betty can mow a lawn in 120 minutes. bullwinkle can mow the same lawn in 40 minutes. how long does it take for both betty and bullwinkle to mow the lawn if they are working together? express your answer as a reduced fraction.



Answer :

sqdancefan

Answer:

  30 minutes

Step-by-step explanation:

You want to know how long it takes for Betty and Bullwinkle to mow the lawn working together, if it takes them 120 minutes and 40 minutes, respectively, when they work separately.

Sum of rates

Each minute, Betty mows 1/120 of the lawn, and Bullwinkle mows 1/40 of the lawn, for a total of ...

  1/120 +1/40 = 1/120 +3/120 = 4/120 = 1/30 . . . . of the lawn

The entire lawn is 30/30 of the lawn, so will take 30×(1 minute) = 30 minutes to mow.

Working together, the mowing takes 30 minutes.

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