Question

It takes Alexandra 2 hours and 44 minutes to cut the grass. Austin needs 3 hours and 14 minutes to cut the grass. If they work together, how long will it take them to cut the grass?

Please show work! :)

Answer 1

For problems such as this, it can be handy to remember that
.. 1/(1/a +1/b) = ab/(a +b)

The time required to do a job is the inverse of the rate at which the job is done. Rates are added when people work together (in math problems, not in real life).

(2:44)*(3:14)/(2:44 +3:14) = 1:28:52.3

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2:44 = 41/15 hours = 82/30 hours
3:14 = 97/30 hours
Using the formula above, we have a "working together" time of
.. (82/30)*(97/30)/(82/30 +97/30) = 82*97/(30*179) = 3977/2685 . . . hours
.. = 1 hour 28 156/179 minutes
.. = 1 hour 28 minutes 52 52/179 seconds

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Learn to use the fraction functions on your calculator. They can be very helpful.