What is the equation for 1/3 of the time to paint a room?

If the a and b of your formula mean how many hours it takes each

person, like a = 2 and b = 1, then the formula gives 3/2 or 1 hour and

30 minutes.  This is not reasonable, since one of the painters alone

could do it in 1 hour.

Actually, your formula is UPSIDE DOWN. It should be (a*b)/(a+b).

Here's why.

Let h be the number of hours it takes for the two of them to do it

together. The first person could do it all in a hours, but can paint

only a fraction of the wall working h hours. Assuming a constant rate

of painting, that fraction is h/a. That is, the first painter will

paint h/a of the wall in h hours.  

Similarly, the second painter will paint h/b of the wall in that time.

So, when will they be done? When the whole wall is painted, which

happens whenever those 2 fractions add up to 1.  

You need to solve the following equation:

 (h/a) + (h/b) = 1  

     h*b + h*a = a*b           Multiplying through by a*b

       h*(b+a) = a*b           Factoring out h

             h = (a*b)/(a+b)   Dividing both sides by b+a

Okay, now say 3 painters could do it in a hours, b hours or c hours,

respectively. Let h be the number of hours they all must work to get

it all painted. The first painter finishes h/a of the wall in that

amount of time. The other 2 painters manage to paint h/b of the wall

and h/c of the wall in that time.  Since h is the time to finish the

job, all 3 of these fractions must add up to the whole wall, or 1.  

So you have the equation:

       h     h     h        

      --- + --- + ---  =  1

       a     b     c    

Solve this for h (start by multiplying through by a*b*c) and you will

get the generalized formula for 3 painters. It's not the formula you

wrote above but I think you can finish it off.

I hope this helps.      

Step-by-step explanation:

c.

step-by-step explanation:

because first you have to add the 4x, 9x, and the 7x together and you get 20x and then you add the last numbers up and you get 5and then you put the subtraction sign in there and that's how you get the answer.

answer: median

step-by-step explanation:

the median is the middle value when a data set is ordered from least to greatest