It takes Sarah as long to paddle 10 miles downstream on a river flowing at 3 mph as it does to paddle 12 miles down a river flowing at 4 mph. How fast does Sarah paddle in still water?
A) 4 mph
B) 3 1/2 mph
C) 3 mph
D) 2 1/2 mph
E) 2 mph
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shankar.ashwin
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shankar.ashwin
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knight247
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Lets Sarah's speed be x under normal circumstances.
For River A
Distance=10
Speed=x+3
Time=10/(x+3)
For River B
Distance=12
Speed=x+4
Time=12/(x+4)
Both times are given to be equal so
10/(x+3)=12/(x+4)
x=2
Her speed is 2mph in still water. Hence E
For River A
Distance=10
Speed=x+3
Time=10/(x+3)
For River B
Distance=12
Speed=x+4
Time=12/(x+4)
Both times are given to be equal so
10/(x+3)=12/(x+4)
x=2
Her speed is 2mph in still water. Hence E
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mehrasa
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sarah's velocity= still water speed + river flow (boat speed, if any)LalaB wrote:what does it mean x+3 x +4?? why??
Sarah's velocity in downstream = X+3
and in the upstream route ==> Sarah's velocity is X+4
since the time of upstream=time of downstream ==> D/X+3=D/X+4 on the other hand, distance for downstream and upstream is 10 and 12 ==> 10/x+3 = 12/x+4 ==> x=2 which is still water velocity
