SOLUTION: Katie can bicycle 69 miles in the same time as it takes her to walk 21 miles. She can ride 8 mph faster than she can walk. How fast can she walk

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Question 1032108: Katie can bicycle 69 miles in the same time as it takes her to walk 21 miles. She can ride 8 mph faster than she can walk. How fast can she walk
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Let +s+ = her walking speed
+s+%2B+8+ = her biking speed
Let +t+ = her time in hrs for
both walking and biking
--------------------------
Equation for walking:
(1) +21+=+s%2At+
Equation for biking:
(2) +69+=+%28+s+%2B+8+%29%2At+
--------------------
(1) +t+=+21%2Fs+
Substitute this into (2)
(2) +69+=+%28+s+%2B+8+%29%2A%28+21%2Fs+%29+
(2) +69+=+21+%2B+168%2Fs+
(2) +48+=+168%2Fs+
(2) +s+=+168%2F48+
(2) +s+=+3.5+
-------------------
Her speed walking is 3.5 mi/hr
-------------------
check:
(1) +t+=+21%2Fs+
(1) +t+=+21%2F3.5+
(1) +t+=+6+
and
(2) +69+=+%28+s+%2B+8+%29%2At+
(2) +69+=+%28+3.5+%2B+8+%29%2A6+
(2) +69+=+11.5%2A6+
(2) +69+=+69+
OK