A boat's speedometer reads 20km per hour going downstream and it reaches its destination in 3/4 of an hour. If the return trip takes on hour at the speed of 20km per hour, how fast is the current?
Can u solve and explain how you did it?
2007-02-04 20:38:02 · 11 answers · asked by Anonymous in Science & Mathematics ➔ Mathematics
1/4 of 20 which is 5km an hour because the boat takes 15mins extra to get back.
2007-02-04 20:41:30 · answer #1 · answered by Anonymous · 0⤊ 1⤋
Let current speed be x km / h
Downstream speed = 20 + x km/h and time = 3/4 hour
Distance, D = (3/4)(20 + x) = 15 + 3x/4
Upstream speed = 20- x and time = 1 hour
Distance D = 1 x (20 - x) = 20 - x
20 - x = 15 + 3x/4
5 = 7x/4
7x = 20
x = 20/7 km / h = 2.86 km / h
Current is 2.86 km / h
2007-02-04 21:51:44 · answer #2 · answered by Como 7 · 0⤊ 0⤋
Here's a clue. If the speed of the current is c, then the boat's speed is 20+c when it is going downstream, and 20-c when it is going upstream.
Here's another clue:
Distance = Speed * Time
2007-02-04 20:44:21 · answer #3 · answered by Gnomon 6 · 0⤊ 0⤋
Let speed of current be x
Distance covered going downstream=3/4(20+x)
Same distance coming upstream=(20-x)
60+3x/4=20-x
60+3x=80-4x
7x = 20
therefore,x =20/7 i.e.2.86km/h
2007-02-04 22:56:35 · answer #4 · answered by ABHINEET N 1 · 0⤊ 0⤋
20/7 kmph is the answer
the distance is constant
let speed of stream be =x
downstream, speed =20+x because the current assists the boat
this is covered in 3/4 hrs
thus distance = speed*time
=(20+x)*0.75
now
upstream, speed =20-x
time = 1hour
thus as before,
distance =(20-x) km
both the distances are equal
so equate them
that is:
(20+x)*3=4*(20-x)
x comes out to be
20/7 kmph
2007-02-04 20:48:03 · answer #5 · answered by parth s 1 · 1⤊ 0⤋
(20km + current) times .75 = distance
return = 1hr times (20km-current)
so both are equal distances - therefore
(20km + X) times .75 = 20km - X
15 km + .75 x = 20km - x....add X to both sides
15 km + 1.75 X = 20km......subtract 15 km from both sides
1.75x = 5 km.....divide both sides by 1.75
and u can finish up from here!
tada!
2007-02-04 20:45:42 · answer #6 · answered by tom4bucs 7 · 0⤊ 0⤋
d = 3(20 + c)/4 = 1(20-c)
3c + 60 = 80 - 4c
7c = 20
c = 20/7 kph = 2.86 kph
2007-02-04 20:55:07 · answer #7 · answered by Helmut 7 · 0⤊ 0⤋
(V1+V2 ) 3/4 =distance=(V3-V2) 1 hr
(20+V2) 3/4 = (20-V2) 1
20 3/4 +V2 3/4 = 20-V2
V2 (3/4 +1) = 20( 1- 3/4)
V2 7/4 = 20 1/4
7 V2 =20
V2 =20/7 =2.85 km per hr
2007-02-04 22:11:38 · answer #8 · answered by Anonymous · 0⤊ 0⤋
a million. replace a million for x interior the equation and remedy. you should get 210 million 2. replace 2 hundred for x interior the equation and remedy. 3. replace 5 for t interior the equation and remedy 4. Take the fellow dosage divide it through 3 and upload 9. What grade are you in?
2016-11-25 03:10:35 · answer #9 · answered by Anonymous · 0⤊ 0⤋
let x= speed of the boat in still water
let y= speed of the current
D R T
upstream 20 x-y one hour
downstream 20 x+y 45 min (60*3/4) or .75
D=RT
1(x-y)=20
.75 (x+y)=20
____________
x-y=20
.75x+.75y=20
____________
.75(x-y)=20
.75x+.75y=20
____________
.75x-.75y=20
.75x+.75y=20
____________ (cancel)
1.5x=40
x=26.67
substitute
26.67-y=20
-y=20-26.67
-y=-6.67
y=6.67
the speed of the current is 6.67 km/hr...
i hope you get it...
2007-02-04 21:44:34 · answer #10 · answered by joy14 1 · 0⤊ 0⤋