<PRE><B>Question 126677</B>
Ann regularly swam .4 km in 20 min at the school pool. Swimming in a river against the current, she swam .25 km in the same time it took Ann to swim .75 km with the current.
: 
Find the speed of the current and the time it took Ann to swim.
:
Find her speed in km/h
.4 in 20 min = 3 * .4 = 1.2 km/hr
:
Let x = speed of the current in km/hr
:
Speed upstream = (1.2 - x}
Speed downstream = (1.2 + x)
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Write a time equation: (Time = distance/speed
:
Upstream time = downstream time
{{{.25/((1.2-x))}}} = {{{.75/((1.2+x))}}}
Cross multiply and you have:
.25(1.2+x) = .75(1.2-x)
:
.3 + .25x = .9 - .75x
:
.25x + .75x = .9 - .3
:
1x = .6 km/hr is the current
;
:
Find the time she swam:
:
Speed upstream: 1.2-.6 = .6 km/hr
Speed downstream: 1.2+.6 = 1.8 km/hr
:
.25/.6 = .41667 * 60 = 25 min( converting hrs to min)
also
.75/1.8 = .41667 * 60 = 25 min also, confirming our solutions
:
Did this help you understand this problem? Any questions?

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