Jack usually mows his lawn in 4 hours. Marilyn can mow the same yard in 5 hours. How much time would it take for them to mow the lawn together?
1/t= 1/4 + 1/5,
1/t = 5/20 + 4/20 = 9/20,
t = 20/9 = 2.2 hours.
Or
t = 4*5 / (4+5) = 20/9 = 2.2 hours.
To find out how much time it would take for Jack and Marilyn to mow the lawn together, we can use the concept of work rates.
Let's calculate their work rates first. Jack can mow the lawn in 4 hours, so his work rate is 1/4 of the lawn per hour. Similarly, Marilyn can mow the lawn in 5 hours, so her work rate is 1/5 of the lawn per hour.
To calculate how much of the lawn they can mow together in one hour, we can add their individual work rates. In this case, 1/4 + 1/5 = 9/20.
This means that together, Jack and Marilyn can mow 9/20 of the lawn in one hour.
To find out the time it would take for them to mow the entire lawn together, we can divide the total work required (which is 1 complete lawn) by their combined work rate.
1 divided by 9/20 is equal to 20/9.
Therefore, it would take them approximately 2 hours and 13 minutes to mow the lawn together.