Gone fishing. Debbie traveled by boat 5 miles upstream to fish in her favorite spot. Because of the 4-mph current, it took her 20 minutes longer to get there than to return. How fast will her boat go in still water?

Grayson Pierce

Grayson Pierce

Answered question

2022-07-27

Gone fishing. Debbie traveled by boat 5 miles upstream to fish in her favorite spot. Because of the 4-mph current, it took her 20 minutes longer to get there than to return. How fast will her boat go in still water?

Answer & Explanation

Killaninl2

Killaninl2

Beginner2022-07-28Added 20 answers

Let x = to the speed of her boat on stillwater
so 5/x = the time it took withoutcurrent
and 5/(x-4) = the time it took withcurrent
and the difference between with and without current is 20 mins,which is 1/3 hour
so we can set an equation
5 x = 5 x 4 + 1 3
time on still water = time with current + 1/3hour(20mins)
then just solve for x
5 x = 5 x 4 + 1 3
5 x = 15 + x 4 3 x 12 simplifythe right side
15 x 60 = 15 x + x 2 4 x crossmultiply
15 x 60 = 15 x + x 2 4 x 0 = x 2 4 x + 60 add 60 and minus 15x both sides
0=(x+6)(x-10) foil the quadratic equation
x=10 ,-6 solve for x
speed can only be positive so x = 10 mphis the only answer
check: 5/10 = 1/2 ,it takes 1/2hours(30mins) on still water
5/(10-4) = 5/6, it take 5/6hours(50mins) with current on water
50mins - 30mins = 20mins longer

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