SOLUTION: norma can row her boat 12 miles in the same time as it takes Marietta to cover 36 miles in her motorboat. if marietta's boat travels 15mph faster than norma's boat, then how fast i

Algebra ->  Polynomials-and-rational-expressions -> SOLUTION: norma can row her boat 12 miles in the same time as it takes Marietta to cover 36 miles in her motorboat. if marietta's boat travels 15mph faster than norma's boat, then how fast i      Log On


   

Question 677539: norma can row her boat 12 miles in the same time as it takes Marietta to cover 36 miles in her motorboat. if marietta's boat travels 15mph faster than norma's boat, then how fast is norma rowing her boat.
I know i have to use time=rate divided by distance. I just have no idea where to start.

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
You need 2 equations- one for Norma
and one for Marietta
Let +t+ = time for both
Let +s+ = the speed of Norma's boat
+s+%2B+15+ = speed of Marietta's boat
---------------------------------
Norma's equation:
(1) +12+=+s%2At+
Marietta's equation:
(2) +36+=+%28+s+%2B+15+%29%2At+
---------------------
(2) +36+=+s%2At+%2B+15t+
Substitute (1) into (2)
(2) +36+=+12+%2B+15t+
(2) +15t+=+24+
(2) +t+=+1.6+
and, since
(1) +12+=+s%2At+
(1) +12+=+s%2A1.6+
(1) +s+=+7.5+
Norma is rowing at 7.5 mi/hr
check:
(2) +36+=+%28+s+%2B+15+%29%2At+
(2) +36+=+%28+7.5+%2B+15+%29%2At+
(2) +36+=+22.5%2At+
(2) +t+=+36%2F22.5+
(2) +t+=+1.6+
OK