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