SOLUTION: Jake drives a tractor from one town to another, a distance of 130 kilometers. He drives 9 kilometers per hour faster on the return trip, cutting 1 hour off the time. How fast does

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Question 990270: Jake drives a tractor from one town to another, a distance of 130 kilometers. He drives 9 kilometers per hour faster on the return trip, cutting 1 hour off the time. How fast does he drive each way?

Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +t+ = time in hrs for the trip to town
+t+-+1+ = time in hrs for return trip
Let +s+ = his speed in km/hr for the trip to town
+s+%2B+9+ = his speed in km/hr for return trip
---------------------------------------------
Going to town:
(1) +130+=+s%2At+
Return trip:
(2) +130+=+%28+s+%2B+9+%29%2A%28+t+-+1+%29+
-----------------------------
(1) +t+=+130%2Fs+
and
(2) +130+=+%28+s+%2B+9+%29%2A%28+130%2Fs+-+1+%29+
Multiply both sides by +s+
(2) +130s+=+%28+s+%2B+9+%29%2A%28+130+-+s+%29+
(2) +130s+=+130s+%2B+1170+-+s%5E2+-+9s+
(2) +s%5E2+%2B+9s+-+1170+=+0+
Use quadratic formula
+s+=+%28+-b+%2B-+sqrt%28+b%5E2+-+4%2Aa%2Ac+%29%29+%2F+%282%2Aa%29+
+a+=+1+
+b+=+9+
+c+=+-1170+
+s+=+%28+-9+%2B-+sqrt%28+9%5E2+-+4%2A1%2A%28-1170%29+%29%29+%2F+%282%2A1%29+
+s+=+%28+-9+%2B-+sqrt%28+81+%2B+4680+%29%29+%2F+2+
+s+=+%28+-9+%2B-+sqrt%28+4761+%29%29+%2F+2+
+s+=+%28+-9+%2B+69+%29+%2F+2+
+s+=+60%2F2+
+s+=+30+
+s%2B+9+=+39+
He drives 30 km/hr going to town
He drives 39 km/hr returning from town
-------------------------------------
check:
(1) +t+=+130%2Fs+
(1) +t+=+130%2F30+
(1) +t+=+13%2F3+ hrs
and
(2) +130+=+%28+s+%2B+9+%29%2A%28+t+-+1+%29+
(2) +130+=+39%2A%28+t+-+1+%29+
(2) +130+=+39t+-+39+
(2) +39t+=+169+
(2) +t+=+169%2F39+
(2) +t+=+%28+13%2A13+%29+%2F+%28+3%2A13+%29+
(2) +t+=+13%2F3+ hrs
OK