Sophie and Simon are peeling a pile of potatoes for lunch in the cafeteria. Sophie can peel all the potatoes by herself in 45 minutes, while it would take Simon 30 minutes to do the job working alone. If Sophie and Simon work together to peel the potatoes, how long will it take them?
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Step-by-step explanation:
Write down the efficiency of each as follows
in 1 minute Sophie can do 1/45 th of the work (assumed as 1 unit)
in 1 minute Simon cna do 1/30 th of the work (assumed as 1 unit)
so together they can do 1/45 + 1/30 = 5/90 = 1/18th of the work
therefore to do 1 unit of work together they will take
1 unit of work / (1/18) hence 18 minutes
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