SOLUTION: Joseph does the laundry in 15 minutes. Mark takes 4 minutes more to do the laundry on his own than when he does it with Joseph. How long does it take when Mark and Joseph do the la

Algebra ->  Equations -> SOLUTION: Joseph does the laundry in 15 minutes. Mark takes 4 minutes more to do the laundry on his own than when he does it with Joseph. How long does it take when Mark and Joseph do the la      Log On


   

Question 1006274: Joseph does the laundry in 15 minutes. Mark takes 4 minutes more to do the laundry on his own than when he does it with Joseph. How long does it take when Mark and Joseph do the laundry together?
(I don't know where to start! - thank you!)
Answer by MathTherapy(10552) About Me  (Show Source):
You can put this solution on YOUR website!

Joseph does the laundry in 15 minutes. Mark takes 4 minutes more to do the laundry on his own than when he does it with Joseph. How long does it take when Mark and Joseph do the laundry together?
(I don't know where to start! - thank you!)
Let time it takes both, be B

Then both can do 1%2FB of laundry in 1 minute 

Mark can do laundry in B + 4 minutes, or 1%2F%28B+%2B+4%29 of laundry in 1 minute

Joseph can do laundry in 15 minutes, or 1%2F15 of laundry in 1 minute

We then get: 1%2F%28B+%2B+4%29+%2B+1%2F15+=+1%2FB

15B + B(B + 4) = 15(B + 4) ------ Multiplying by LCD, 15B(B + 4)

15B+%2B+B%5E2+%2B+4B+=+15B+%2B+60

19B+%2B+B%5E2+=+15B+%2B+60

B%5E2+%2B+19B+-+15B+-+60+=+0

B%5E2+%2B+4B+-+60+=+0

(B - 6)(B + 10) = 0 

B, or both can do laundry in: highlight_green%286%29 minutes	   OR	         B = - 10 (ignore)