Math-they Have To 800 Bricks To Complete The Job. How Many Hrs After He Began Working Did They Finish The Job?

3 Responses to “Math-they Have To 800 Bricks To Complete The Job. How Many Hrs After He Began Working Did They Finish The Job?”

1. Rec

   December 26, 2011 at 8:32 pm

   Sergei can lay 45 bricks/hr
   his boss can lay 60 bricks/hr
   given that Sergie has already been working for 3 hrs. During that time he has laid 45 * 3 = 135 bricks
   let t be the time it takes for them to finish laying 800 bricks since the time his boss joins him
   135 + 45t + 60t = 800
   105t = 665
   t = 6 1/3 hrs OR 6 hrs 20 min
   so the total time is 9 hrs and 20 min <== answer

   #56942
2. always_c

   December 27, 2011 at 2:34 am

   135 + (60 + 45)(x – 3) =
   135 + 105(x – 3) = n where x is the time in hours and n is the number of bricks
   n = 135 + 105x – 315
   n = 105x – 180
   So if they’re laying 800 bricks
   800 = 105x – 180
   800+180 = 105x
   980 = 105x
   x = 980/105
   x = 9.33
   x = 9h 20 min
   If you want to double check that:
   800 bricks – 135 (sergei already laid) = 665 Bricks.
   45/h + 60/h = 105/h
   665/105 = t
   t = 6.33 = 6h 20 min + 3 hours sergei has already been working = 9h 20 min

   #56943
3. Jenna T

   December 27, 2011 at 5:35 am

   7 hours 12 minutes

   #56944