Alex and David had a bicycle race.Alex cycled at a speed of 12km/h and David cycled at a speed of 16km/h.David let Alex start 40 minutes before him.At what time would David catch up with Alex if Alex started at 8.00a.m.
2006-09-22 21:43:44 · 13 answers · asked by tocatchtheuncatchableii 3 in Science & Mathematics ➔ Mathematics
d = rt
let x be the time of david
x - 40 be the time of alex
x(16km/hr) = (x-40)(12)
16x = 12x - 480
480 = 6x
x = 80 minutes
they will meet at 9:20 am
goodluck ^_^
2006-09-22 21:54:53 · answer #1 · answered by ettezzil 5 · 1⤊ 0⤋
Alex cycles at 12km/h
David cycles at 16km/h
Alex starts 40 minutes earlier
Thus, he has a (12/60)*40 = 8 km headstart
Ground gained on Alex by David per hour = 16-12 = 4 km
8 / 4 = 2
Alex starts at 8 am, thus David starts at 8:40 am
8:40 am + 2 hours --> 10:40 am
David catches up with Alex at 10:40 am
2006-09-23 05:01:19 · answer #2 · answered by Ashley 2 · 0⤊ 0⤋
Valex = 12 Km/h
Vdav = 16 Km/h
talex-tdav = 40 min = 2/3 h
david catch alex so d=Dalex=Ddav
Dalex = Ddav =>
Valex * talex = Vdav * tdav =>
12talex = 16 (talex-2/3) =>
12talex = 16talex - (32/3) =>
4 talex = 32/3 => talex = 8/3 hours = 2 hours and 20 min
David catch Alex at 10:20 am
2006-09-23 05:00:19 · answer #3 · answered by paymanns 2 · 0⤊ 0⤋
Alex Started 40 mins earlier.Find how far he went by that time:
12 x (40/60)= 8 kms .Alex is 8 kms ahead.
David cycles 16-12= 4 kms faster.So he is going 4 kms more than Alex per hour. SO he will catch Alex 8/4=2 hours later after he start to cycle.And that makes : 08.00+00.40+2.00+= 10.40 am.
2006-09-23 05:15:02 · answer #4 · answered by Leprechaun 6 · 0⤊ 0⤋
alright, lemme see...
in forty minutes, Alex would be 12 x 40 / 60 = 8 km ahead of David
now in one hour, David gets 16 - 12 = 4 km closer to Alex
so, David catches up with Alex in two hours, which is 10.40 am
(mind the forty minutes David waited for, which the guy before me forgot to take into account...)
2006-09-23 04:53:08 · answer #5 · answered by Anonymous · 0⤊ 0⤋
Answer: 10:40
8+x=12(40+t)
8+x=16t
12(40+t)=16t
480+12t=16t
480=4t
t=120 minutes=2 hours
8:40+2=10:40
2006-09-23 04:53:13 · answer #6 · answered by iyiogrenci 6 · 0⤊ 0⤋
11:00 A.M all of the above are correct in calcualting totalt time to catch up that is 160 mins but as its 40 mins headstart , it wll be 11 am
2006-09-23 06:02:57 · answer #7 · answered by Anonymous · 0⤊ 0⤋
Alex
S=12 Km/h
t=40 mins = 40/60= 0.67 hours(converted minutes into hours)
d=?
s=d/t = 12=d/0.67 => 12*0.67= d therefore d= 8.04 km
David
s=16 km/h
t=?
d=8.04 km (worked out above)
s=d/t= 16=8.04/t=> t=8.04/16 therefore t=0.50 hours
60/0.50=120 minutes (converting time taken back into minutes)
120+840=10:00 a.m <<<<---Answer
2006-09-23 05:13:57 · answer #8 · answered by Farhan 3 · 0⤊ 0⤋
d= vt
d = distance .......v = speed......t = time
when David catch Axel then
d1 = d2
v1t1 = v2t2
12 t1 = 16 t2
3 t1 = 4 t2
t2 = ¾ t1
where David started â
hours later
t2 = t1 - â
¾ t1 = t1 - â
t1 - ¾ t1 = â
¼ t1 = â
t1 = 8/3
t1 = 2 â
hours
so David will catch Axel at 10:40 Am
2006-09-23 05:08:11 · answer #9 · answered by M. Abuhelwa 5 · 0⤊ 0⤋
d=r*t
(16 km/hr)*(t-40 min*(1 hr/60 min)=(12 km/hr)*t
16t-32/3=12t
48t-32=36t
12t=32
t=32/12 hr =2 hr 40 min
8:00+2:40=10:40
2006-09-23 04:58:39 · answer #10 · answered by Helmut 7 · 0⤊ 0⤋