When Sandy and Allen's mother decorates the house for a holiday by herself, it takes her 5 hours. When both Sandy and Allen help, the three can finish the job in 2.5 hours. When only Allen helps his mother decorate, it takes the two 3.5 hours. How long would it take Sandy to decorate the house by herself?

8 3/4

Step-by-step explanation:

time for all work:

Mother - 5 hours

Mother + Sandy + Allen - 2.5 hours

Mother + Allen - 3.5 hours

Sandy - x

In 1 hour

Mother - 1/5

Mother + Sandy + Allen - 2/5

Mother + Allen - 2/7

Sandy - 1/x

(M+S+A) - S = (M+A)

2/5 - 1/x = 2/7

solve equation

x = 8 3/4 hours

Hope this helps :)

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