SOLUTION: A cistern can be filled by two pipes. The small pipe will take 24 minutes longer than the bigger pipe to fill the cistern alone.The small pipe alone will take 32 minutes longer to

Algebra ->  Rate-of-work-word-problems -> SOLUTION: A cistern can be filled by two pipes. The small pipe will take 24 minutes longer than the bigger pipe to fill the cistern alone.The small pipe alone will take 32 minutes longer to       Log On


   



Question 891131: A cistern can be filled by two pipes. The small pipe will take 24 minutes longer than the bigger pipe to fill the cistern alone.The small pipe alone will take 32 minutes longer to fill the cistern than when the two pipes are working together. how long will it take the bigger pipe to fill the cistern alone??
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +b+ = time in minutes for the big
pipe to fill the cistern
Let +t+ = time in minutes for both
pipes filling together to fill cistern
--------------------------------
Small pipe's rate of filling = +1+%2F+%28+b+%2B+24+%29+
Big pipes rate of filling = +1%2Fb+
-------------------------------
With both pipes filling:
+1%2Fb+%2B+1%2F%28+b+%2B+24+%29+=+1%2Ft+
Multiply both sides by +b%2A%28+b+%2B+24+%29%2At+
+t%2A%28+b+%2B+24+%29+%2B+t%2Ab+=+b%2A%28+b+%2B+24+%29+
+t%2A%28+2b+%2B+24+%29+=+%28+b%5E2+%2B+24b+%29+
+t+=+%28+b%5E2+%2B+24b+%29+%2F+%28+2b+%2B+24+%29+
--------------------------------
+b+%2B+24+=++%28+b%5E2+%2B+24b+%29+%2F+%28+2b+%2B+24+%29++%2B+32+
+%28+b+%2B+24+%29%2A%28+2b+%2B+24+%29+=+b%5E2+%2B+24b+%2B+32%2A%28+2b+%2B+24+%29+
+2b%5E2+%2B+48b+%2B+24b+%2B+576+=+b%5E2+%2B+24b+%2B+64b+%2B+768+
+b%5E2+%2B+72b+%2B+576+=+88b+%2B+768+
+b%5E2+-+16b+-+192+=+0+
-------------------------
Use quadratic equation:
+b+=+%28-B+%2B-+sqrt%28+B%5E2-4%2AA%2AC+%29%29%2F%282%2AA%29+
+A+=+1+
+B+=+-16+
+C+=+-192+
-----------------
+b+=+%28-%28-16%29+%2B-+sqrt%28+%28-16%29%5E2+-+4%2A1%2A%28-192%29+%29%29%2F%282%2A1%29+
+b+=+%28+16+%2B-+sqrt%28+256+%2B+768+%29%29+%2F+2+
+b+=+%28+16+%2B-+sqrt%28+1024+%29%29+%2F+2+
+b+=+%28+16+%2B+32+%29+%2F+2+
+b+=+48%2F2+
+b+=+24+
-------------
It will take the big pipe 24 minutes
filling alone
--------------
check:
+1%2Fb+%2B+1%2F%28+b+%2B+24+%29+=+1%2Ft+
+1%2F24+%2B+1%2F%28+24+%2B+24+%29+=+1%2Ft+
+1%2F24+%2B+1%2F48+=+1%2Ft+
+1%2Ft+=+3%2F48+
+t+=+48%2F3+
+t+=+16+
-------------
This checks out- +b+%2B+24+=+24+%2B+24+ is
the time for the small pipe filling alone
+48+ minutes is +32+ minutes longer than
+t+=+16+ ( both pipes filling together )