Answer:
1.875 hours
Step-by-step explanation:
The first person completes the project in 3 hours
Let's assign 1 to the project.
This means the unit rate per hour is 1/3
The second person completes the same project in 5 hours
This means the unit rate per hour is 1/3.
Their unit rates of working is additive, this means they work simultaneously. First person does not stop working for second person to start working.
Total rates = 1/3 + 1/5 = 8/15
Let t hours be the time it takes both of them
If it takes t hours to do the project together, the unit rate of working together will be 1/t
Equating both unit rates,
8/15 = 1/t
t = 15/8 = 1.875 hours
