If Jim Roller can paint a room in 3 hours while John Brush would take 5 hours, how long will they take if they work together?

Question

anonymous · Answer

anonymous · Answer

a;1/8 hour
b;8/15 hour
c; 7/8 hours

anonymous · Answer

@RadEn

anonymous · Answer

What class is this?

anonymous · Answer

math

anonymous · Answer

I know, but what level of math?

anonymous · Answer

i need help

anonymous · Answer

You need to make a system of equations.

anonymous · Answer

Let, $t$ be the time it takes to paint the room.  $r$ is the rate that Roller to paints it, $b$ is the rate that Brush paints it.

anonymous · Answer

We know that  $$
3r = 5b
$$

anonymous · Answer

We also know that $$
(r+b)t = 3r = 5b
$$

anonymous · Answer

First solve for $r$ in terms of $b$ $$
3r=5b\implies r = \frac{5}{3}b
$$Now plug it into equation 2 $$
\left(\frac{5}{3}b+b\right)t=5b
$$

anonymous · Answer

Then solve for $t$.

raden · Answer

shorcut way : 
3*5/(3+5) = 15/8

long way :p 
v1+v2 = x/3 + x/5 = 8x/15 = x/(15/8)
so, if they work together will take 15/8 hours

raden · Answer

no correct options there