CAR RALLY: Heidi and Kelly drove in an antique car rally. Kelly left a checkpoint at 09:00 travelling at 45 km/h. One hour later, Heidi left the same checkpoint travelling at 50 km/h. At what time did Heidi overtake Kelly?
2007-03-29 06:33:12 · 9 answers · asked by Anonymous in Science & Mathematics ➔ Mathematics
We can follow the race from the checkpoint on. Lets say, Heidi overtook Kelly at the distance s. Kelly's time is t, then Heidi's time is (t+1), because at the checpoint their time difference was 1 hour.
Kelly's way: s=45*(t+1)
Heidi's way: s=50*t
Implicates:
45*(t+1) =50*t =>
45*t + 45 = 50*t =>
45 = 50*t -45*t =>
45 = 5*t =>
t = 45/5 =>
t = 9
The answer is 9 hours.
2007-03-29 06:53:34 · answer #1 · answered by Hurricane 2 · 0⤊ 0⤋
Kelly gets an hour's head start. Because her speed is 45 km/hr, Kelly is 45 km ahead of Heidi when Heidi starts.
Because Heidi is going 5 km/hr faster, she gains 5 km on Kelly every hour. So it takes her 9 hours to make up the 45 km.
Therefore she catches Kelly at 19:00, or 7 PM.
2007-03-29 13:41:09 · answer #2 · answered by pontcb 2 · 0⤊ 0⤋
Kelly departer the check point at 09:00 am
Heidi departed the chedk point at 10:00am
on kelly 10 th hour driven 450 miles
Heidi on the 9 hour driven 450 miles
Kelly 10 hour is 18:00 hours which is 6 pm
Heidi 9 hour is 18:00 hour which is 6pm
at 6 pm heidi caught and overtake kelly
- - - - - - - - s-
2007-03-29 14:38:56 · answer #3 · answered by SAMUEL D 7 · 0⤊ 0⤋
I am assuming Kelly left the checkpoint at 9am and assuming both of them drove along the same route the entire time.
Heidi overtakes Kelly just after both of them cover the same distance.
Hence, D=45*(y+1)=50*y, where y is time in hours
rearranging
45=5*y
or y = 9 hrs.
So, Heidi overtakes Kelly just after 7 pm.
2007-03-29 13:43:54 · answer #4 · answered by naveen 1 · 0⤊ 0⤋
There is a better way to solve this but I would suggest that you start by noting the distance traveled by each driver as a function of time:
Time K H
10 45 0
11 90 50
12 135 100
1 180 150
etc.
Hopefully once you get the answer you will see the faster way to solve it and will do better on the next problem.
2007-03-29 13:39:28 · answer #5 · answered by jiyuztex 2 · 0⤊ 0⤋
you have the find the LCM. a multiple in which both numbers are factors.
this number is 450
50*9=450 45*10=450
so the lost hour is compensented by the extra 5km.hr after 10hours!
so basically after 19.00!
2007-03-29 13:51:34 · answer #6 · answered by cute-goddess 5 · 0⤊ 0⤋
if it was in a rally wouldnt she have finished the stage before heidi left?
2007-03-29 13:42:40 · answer #7 · answered by gogreenordie 1 · 0⤊ 0⤋
Story math problems. Yuck! Good luck
2007-03-29 13:41:34 · answer #8 · answered by Snowflakes 2 · 0⤊ 0⤋
I hated those kind of story math problems. Hope somebody can show you the formula!
2007-03-29 13:40:54 · answer #9 · answered by Inquisitive 4 · 0⤊ 0⤋