Betty can mow a lawn in 60 minutes. Melissa can mow the same lawn in 30 minutes. How long does it take for both Betty and Melissa to mow the lawn if they are working together? Express your answer as a reduced fraction.

  20 minutes

Step-by-step explanation:

Melissa works as fast as two Bettys, so working together, they get the job done at the rate 3 Bettys could do it. That time is (60 minutes)/3 = 20 minutes.

Working together, Betty and Melissa can mow the lawn in 20 minutes.

You can also think in terms of mowing rates as lawns per minute. The total mowing rate is ...

  Betty's rate + Melissa's rate = (1/60 lawns/min) +(1/30 lawns/min)

  = (1/60 +2/60) lawns/min = 1/20 lawns/min

The inverse rate is then ...

  20/1 min/lawn

Together, they take 20 minutes to mow 1 lawn.

answer: the answer is one of

step-by-step explanation:   we are given to write a proper fraction where the whole is divided into an even number of equal parts less than ten, and an odd number of those parts exist.

an even number less than 10 may be one of 2, 4, 6 or 8. so, the whole may be one of these four evens.

now, an odd number of these parts must exist, so the numerator must be an odd number, one of 1, 3, 5 or 7. it cannot be 9 because then the fraction will become improper.

thus, our fraction may be one of the following