help algebra

Let the time to complete the job with 5 workers = T days

So......the total man-days for the job  is  5T

If one additional worker is  hired, the man-days for the job is 6 (T - 8)

So....since the man-days will be the same for the job.....

5T  = 6(T - 8)

5T = 6T - 48

48 = T 

So   the number of man-days to complete the job is   5(48)  = 240

So.....to complete the job 28 days earlier

(number of  workers needed) * ( 48 - 28)  =  240

(number of workers needed)  * (20)   = 240

number of workers needed  = 240 / 20     =    12

So.....(12  - 5) =  7  additional workers should be hired to  complete the job 28 days earlier

How many additional workers should be hired?

Hello Lilliam0216!

I assume the 5 workers can complete the job in around 120 hours.

$\psi =\frac{J}{5\cdot 120h}\\ J=5\cdot 120h\cdot \psi =(5+1)\cdot (120-8)\cdot \psi=(5+x)\cdot (120-28)\cdot \psi\\ 6\cdot 112=(5+x)\cdot 92\\ 672=460+92x\\ x=\frac{672-460}{92}=2.3\color{blue}\to 3\\ 6\cdot t=(5+\color{blue}3)\cdot 92$

$t=\frac{8\cdot 92}{6}=\color{blue}122\frac{2}{3}h$

If the 5 workers completed the work in 122 2/3 hours, 3 additional workers should be hired to save 28 hours.

An additional time specification is absolutely necessary for your question.

  !