If two trains ,travelling at a speed of 72mph and 48 mph respectively, are approaching each other from opposite direction; what is the distance between them 1 minute before the collision ?
A)2 miles
B)3 miles
C)4 miles
D)5 miles
E)none of the above.
The OA is A.
I don't know how to solve this PS question. Experts, could you tell me how? Please.
If two trains ,travelling at a speed of 72mph and 48 mph. .
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They are approaching each other at a combined speed of 72+48 = 120 mph = 2 miles/minute.M7MBA wrote:If two trains ,travelling at a speed of 72mph and 48 mph respectively, are approaching each other from opposite direction; what is the distance between them 1 minute before the collision ?
A)2 miles
B)3 miles
C)4 miles
D)5 miles
E)none of the above.
The OA is A.
I don't know how to solve this PS question. Experts, could you tell me how? Please.
So, since they are 1 minute apart according to the question, at their combined speed of 2 miles/minute:
distance = rate x time > = 2 miles/minute x 1minute = 2 miles A
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Hello M7MBA.
It is easier and faster as regor60 said.
But if you don't know about the combine speed, you can solve it as follows.
Train A travels at 48mph, which is equivalent to 48/60=4/5 miles per minute.
Train B travels at 72mph, which is equivalent to 72/60=6/5 miles per minute.
Suppose that you're in the place where they collisioned.
If you go back 1 minute, then train A move back 4/5 miles and train B moves back 6/5 miles.
So, their distance is equal to 4/5+6/5=10/5=2 miles.
So, the correct answer is A.
I hope this explanation may help you.
I'm available if you'd like a follow up.
It is easier and faster as regor60 said.
But if you don't know about the combine speed, you can solve it as follows.
Train A travels at 48mph, which is equivalent to 48/60=4/5 miles per minute.
Train B travels at 72mph, which is equivalent to 72/60=6/5 miles per minute.
Suppose that you're in the place where they collisioned.
If you go back 1 minute, then train A move back 4/5 miles and train B moves back 6/5 miles.
So, their distance is equal to 4/5+6/5=10/5=2 miles.
So, the correct answer is A.
I hope this explanation may help you.
I'm available if you'd like a follow up.
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I call this a shrinking gap question.M7MBA wrote:If two trains ,travelling at a speed of 72mph and 48 mph respectively, are approaching each other from opposite direction; what is the distance between them 1 minute before the collision ?
A)2 miles
B)3 miles
C)4 miles
D)5 miles
E)none of the above.
When we ADD the speeds of the trains, we get 72 mph + 48 mph = 120 mph
This means, the gap SHRINKS at a rate of 120 miles per HOUR
We can also say that the gap SHRINKS at a rate of 2 miles per MINUTE
What is the distance between them 1 minute before the collision ?
Since the gap SHRINKS at a rate of 2 miles per MINUTE, we can conclude that, 1 minute before the collision, the trains will be 2 miles apart.
Answer: A
Cheers,
Brent
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Since the trains travel toward each other, they WORK TOGETHER to cover the distance between them.M7MBA wrote:If two trains ,travelling at a speed of 72mph and 48 mph respectively, are approaching each other from opposite direction; what is the distance between them 1 minute before the collision ?
A)2 miles
B)3 miles
C)4 miles
D)5 miles
E)none of the above.
When elements work together, ADD THEIR RATES.
Combined rate for the two trains = 72+48 = 120 miles per hour = 2 miles per minute.
Let the TOTAL travel time for the two trains = 1 minute.
Let the faster train start at Point A and the slower train start at Point B.
The question stem becomes:
If it takes 1 minute for the two trains to meet, what is the distance between Point A and Point B?
Since the two trains travel at a combined rate of 2 miles per minute for a total time of 1 minute, the distance between Point A and Point B = rt = 2*1 = 2 miles.
The correct answer is A.
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The distance 1 minute before they collide is the total distance they travel in 1 minute, which is:M7MBA wrote:If two trains ,travelling at a speed of 72mph and 48 mph respectively, are approaching each other from opposite direction; what is the distance between them 1 minute before the collision ?
A)2 miles
B)3 miles
C)4 miles
D)5 miles
E)none of the above.
The OA is A.
I don't know how to solve this PS question. Experts, could you tell me how? Please.
72 x 1/60 + 48 x 1/60
(72 + 48) x 1/60
120 x 1/60
2 miles
Answer: A
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