Question

15. John and Mariano are working on their project. Working alone, John can do it in 3 hours, while Mariano can doit in 5 hours. How long would it take them to complete the project working together?

Answer 1

As per given by the question,

John can do the project in 3 hours,

So,

$\frac{1}{3}$

And, Mariano can do same project in 5 hours.

So,

$\frac{1}{5}$

Now,

Let t is the time to finish the project.

So,

If they work together, then;

$\frac{1}{3}+\frac{1}{5}=\frac{1}{t}$

Now,

Multiply both side by 15t,

So,

$\begin{gathered} \frac{15t}{3}+\frac{15t}{5}=\frac{15t}{t} \\ 5t+3t=15 \end{gathered}$

Then,

$\begin{gathered} 5t+3t=15 \\ 8t=15 \\ t=\frac{15}{8} \\ t=1.87 \end{gathered}$

Hence, 1.87 hours would it take them to complete the project if working together.