Answer:
<em>It takes them 1.875 hours.</em>
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<em>Step-by-step explanation:</em>
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<em>Here, the job is cleaning the house.</em>
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<em>Mom does 1 job in 3 hours.</em>
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<em>In 1 hour, mom does 1/3 of the job.</em>
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<em>Dad does 1 job in 5 hours.</em>
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<em>In 1 hour, dad does 1/5 of the job.</em>
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<em>Mom and dad working together do the job in x hours.</em>
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<em>In 1 hour, mom and dad together do 1/x of the job.</em>
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<em>1/3 + 1/5 = 1/x</em>
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<em>5/15 + 3/15 = 1/x</em>
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<em>8/15 = 1/x</em>
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<em>8x = 15</em>
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<em>x = 15/8 = 1.875</em>
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<em>Answer: It takes them 1.875 hours.</em>
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