Question

The distance between New York City, NY, and Louisville, KY is 720 miles. One morning a train traveling 80 mph left from New York. Two hours later a slower train, traveling at 60 mph, left Louisville. How many hours will the slower train travel for before both trains will arrive at the same point?

Answer 1

Answer:

2 hours

Step-by-step explanation:

Given : The distance between New York City, NY, and Louisville, KY is 720 miles. One morning a train traveling 80 mph left from New York. Two hours later a slower train, traveling at 60 mph, left Louisville.

To find : How many hours will the slower train travel for before both trains will arrive at the same point?

Solution : Let the distance covered by NY is x

and  let the distance covered by KY is y

Total distance covered is  $x+y=720$   ........[1]

→ New York city,

Distance traveled = x

Speed of the train = 80 mph

Time taken = t+2

Formula is $\text{Time}=\frac{\text{Distance}}{\text{Speed}}$

$t+2=\frac{x}{80}$ .......[2]

→ Louisville,

Distance traveled = y

Speed of the train = 60 mph

Time taken = t

Formula is $\text{Time}=\frac{\text{Distance}}{\text{Speed}}$

$t=\frac{y}{60}$ .......[3]

Put the value of t from [3] into [2]

$\frac{x}{80}- \frac{y}{60}=2$  ......[4]

Now, we solve equation [1] and [4],

Put the value of y from [1] and put back in [4], $y=720-x$

$\frac{x}{80}- \frac{y}{60}=2$

$\frac{x}{80}- \frac{720-x}{60}=2$

$\frac{60x-80(720-x)}{80\times60}=2$

$60x-57600+80x=9600$

$140x-57600=9600$

$140x=57600+9600=67200$

$x=\frac{67200}{140}=480$

Put x=480 in [1]

$x+y=720$  

$480+y=720$  

$y=240$  

So, The distance covered by train from New York city is x=480 miles

The distance covered by train from Louisville is y=240 miles.

Now put value of y in [3] to get time,

$t=\frac{y}{60}$

$t=\frac{240}{60}$

$t=4$

So, The time taken by train from Louisville is 4 hr.

The time taken by train from New York city is t+2=4+2=6 hr.

→ 6-4=2 hours will the slower train travel for before both trains will arrive at the same point.