Answer:
It takes them approximately 27 minutes to mow the lawn if they are working together.
Explanation:
Wilma can mow a lawn in 80 minutes. This means she can mow at the rate of 1 lawn in 80 minutes. We can write this rate as R = 1/80
Melissa can mow the same lawn in 40 minutes. This means she can mow at the rate of 1 lawn in 40 minutes. We write the rate as R = 1/40.
Now, if the are working together, we need to determine how long it would take for them to mow a lawn. Let this rate be 1/x.
What we want to find is
1/80 + 1/40 = 1/x
Multiply through by 80, we have
1 + 2 = 80/x
3 = 80/x
Take reciprocals of both sides
x/80 = 1/3
x = 80/3
= 1600 seconds
Approximately 27 minutes