John ran for 1/3 hour and then walked for half an hour at the rate of 3 kph. in all,he had covered 4 km. how fast did he run?
2007-01-22 21:05:41 · 14 answers · asked by annika178 1 in Science & Mathematics ➔ Mathematics
Use the formula: Distance = Speed * Time
While running, d1 = s * (1/3) = s/3
While walking, d2 = 3 * (1/2) = 3/2
Total distance = d1 + d2 = 4
Therefore, s/3 + 3/2 = 4
Now solve for s (his running speed).
Multiplying through by 6 gives :
2s + 9 = 24
Subtracting 9 from both sides gives :
2s = 15
Dividing both sides by 2 gives :
s = 7.5 kph
2007-01-22 22:17:26 · answer #1 · answered by falzoon 7 · 0⤊ 0⤋
Half hour: 1/2
3 Kph: 3
3*1/2=1.5
4-1.5=2.5
John ran 2.5 km in 1/3 of an hour.
solve.
2007-01-23 07:41:01 · answer #2 · answered by Anonymous · 0⤊ 0⤋
ran for 20 minutes @ ? kph
walked for 30 minutes @ 3 kph = 6 kph so in 30 mins 3 km covered.
so running for 20 mins covered 1 km so he also ran at 3 kph
2007-01-23 05:34:45 · answer #3 · answered by paul t 4 · 0⤊ 1⤋
john ran for 1/3 of an hour and walked for 1/2 of an hour so in total, he ran/walked for 5/6 of an hour. He covered 4 kms
During the 1/2 hour, he walked at the rate of 3km per hour.
3km/1hour=xkm/(1/2)hour
3/1=x/(1/2)
x= 3/2 -- or 1.5 kilometers
So he walked 1.5 kilometers of the 4 kms total
4 km - 1.5 = 2.5 km that he ran for in 1/3 of an hour.
2.5 km/(1/3)hr= x km/1
7.5km/hr = x km/hr
So he ran at the speed of 7.5 km per hour
2007-01-23 05:16:33 · answer #4 · answered by Bill F 6 · 1⤊ 0⤋
Half hour at 3 kph = 1.5 km
4 - 1.5 = 2.5 km
Running speed = 2.5 k in 1/3 hour = 7.5 kph
2007-01-25 22:01:02 · answer #5 · answered by Norrie 7 · 0⤊ 0⤋
John walked for 0.5 hours at 3kph, therefore he covered 3 * 0.5 = 1.5 km
Total distance travelled is 4km, so he must have covered 5 - 1.5 = 2.5km running
2.5km in 1/3 of an hour is equivalent to 2.5 * 3 = 7.5kph
7.5kph
2007-01-23 05:54:49 · answer #6 · answered by Tom :: Athier than Thou 6 · 0⤊ 0⤋
if he runs at x km per hour he travels 1/3x km
if he walks at 3 km per hour he travels 1/2of 3 km
so 1/3x + 1/2 of 3 must = 4 km
multiply everything by 6.......6times1/3x = 2x
6times 1/2 of 3 = 3 of 3 = 9
6 times 4 = 24
so 2x + 9 = 24
take 9 from both sides
2x = 15
divide both sides by 2
x = 7and a half...........7.5 Km per hour...running speed
2007-01-24 19:06:00 · answer #7 · answered by blaven 1 · 0⤊ 0⤋
Walked for 0.5 h at 3km/h
Distance = speed x time
Distance walked = 1.5 km
Distance ran = 4 - 1.5 km = 2.5 km
speed = distance/time
Running speed = 2.5/(1/3) km/h = 7.5 km/h
2007-01-23 07:16:38 · answer #8 · answered by Como 7 · 0⤊ 0⤋
he walked for 1/2 hr at a rate of 3km/hr so he walked for 3*1/2 = 1.5 km
distance he ran is = 4km - 1.5km = 2.5km
rate he ran= 2.5/(1/3) = 7.5 kmph
2007-01-23 06:29:42 · answer #9 · answered by Anonymous · 0⤊ 0⤋
use distance = speed x time
total distance = distance ran + diatance walked
4km = (running speed x 1/3h) + (walking speed x 1/2 h)
4km = (running speed x 1/3 h) + (3kph x 1/2 h)
4km = running speed x 1/3h + 3/2 km
running speed = (4km - 3/2km)/ 1/3h
running speed = 15/2kph
ANSWER = 7.5kph
2007-01-23 06:41:02 · answer #10 · answered by swas77 2 · 0⤊ 0⤋