Math CentralQuandaries & Queries


Question from Wade, a parent:

My daughter and I are having problems with this question:
Maggie can mow the lawn in 6 hrs. If her sister, Julie, helps her, it only take 2 hrs. How long
does it take Julie to mow the lawn alone.



You need to think in terms of rates.

Maggie can mow the lawn in 6 hours so she mows at 1/6 of a lawn per hour. You don't know how long it takes Julie to mow the lawn so let's say it takes j hours. Thus Julie mows the lawn at 1/j lawns per hour. Together they can mow the lawn in 2 hours so together their rate is 1/2 a lawn per hour. Thus

1/6 + 1/j = 1/2

Find j.

I hope this helps,

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