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Answer 1 · 2017-12-12T15:02:37

The time it would take for Jack and Marilyn to mow the lawn together will be #2#hours and #55# minutes.

Jack mows the lawn in #5# hours.

That means Jack mows #1/5# th of the lawn in #1 # hour.

Similarly,

Marilyn can mow the same lawn in #7 #hours.

That means, Marilyn mows #1/7# th of the lawn in #1# hour.

So if they work together,

In 1 hour they will mow #1/5 +1/7 # th of the lawn, i.e.:

#=1/5(7/7) + 1/7(5/5)#

#= 7/35+5/35 = 12/35#th of the lawn is mowed in #1# hour.

That means, they will need #35/12# hours to mow the lawn together,i.e.:

#35/12 = 2 11/12# hours.

#11/12#th of an hour =# 11/12 x 60# minutes= #55# minutes.

The time it would take for Jack and Marilyn to mow the lawn together will be #2#hours and #55# minutes.

Answer 2 · 2017-12-12T15:14:08

#2hrs# #55 minutes#

In #5# hrs Jack mows #1# Lawn
So in #1# hr Jack mows #1/5# Lawn

In #7# hrs Marilyn mows #1# Lawn
So in #1# hr Marilyn mows #1/7# Lawn

So we can write together Jack and Marilyn in #1# hr can mow #1/5+1/7=(7+5)/35=12/35# Lawn

So they can mow a Lawn i.e. #1# Lawn in #35/12 hrs=2 11/12hrs#=#2hrs# #55 minutes#