The figure above represents a network of one-way streets.

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The figure above represents a network of one-way streets. The arrows indicate the direction of traffic flow, and the numbers indicate the amount of traffic flow into or out of each of the four intersections during a certain hour. During that hour, what was the amount of traffic flow along the street from R to S if the total amount of traffic flow into P was 1,200 ? (Assume that none of the traffic originates or terminates in the network.)

A. 200
B. 250
C. 300
D. 350
E. 400


OA B

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by henilshaht » Sun Dec 15, 2019 10:50 am
Let's assume the traffic from R to S is x
and traffic from S to P is y.

Now, we know the inward traffic at P is 1200. So,
1200 = 800 + y
y = 400.

At any point, inward traffic will be equal to the outward traffic.
So, using that approach at S, we get the following equation

Inward traffic at S = Outward traffic at S
550 + x = 400 + y
x = 400 + 400 - 550
x = 250

Answer B

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by [email protected] » Wed Jan 01, 2020 6:43 pm
BTGmoderatorDC wrote:Image


The figure above represents a network of one-way streets. The arrows indicate the direction of traffic flow, and the numbers indicate the amount of traffic flow into or out of each of the four intersections during a certain hour. During that hour, what was the amount of traffic flow along the street from R to S if the total amount of traffic flow into P was 1,200 ? (Assume that none of the traffic originates or terminates in the network.)

A. 200
B. 250
C. 300
D. 350
E. 400


OA B

Source: Official Guide
First let's look at intersection P. Since 1,200 cars flow into P and 900 flow out of P northwardly, 300 must flow out of P eastwardly to Q.

Next, let's look at intersection Q. Since 300 + 500 = 800 cars flow into Q and 200 flow out of Q eastwardly, 600 must flow out of Q southwardly to R.

Lastly, let's look at intersection R. Since 600 + 400 = 1,000 cars flow into R and 750 flow out of R southwardly, 250 must flow out of R westwardly to S.

Alternate Solution:

The total traffic flow into P is the sum of the traffic flow from S to P and the traffic flow into P from east, which is 800. Since the total traffic flow into P is given to be 1,200; the traffic flow from S to P must be 1200 - 800 = 400.

We see that the total traffic flow out of S is 400 + 400 = 800. Since the traffic flow into S from south is 550, the traffic between R and S must be 800 - 550 = 250.

Answer: B

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BTGmoderatorDC wrote:
Fri Dec 13, 2019 4:56 pm
Image


The figure above represents a network of one-way streets. The arrows indicate the direction of traffic flow, and the numbers indicate the amount of traffic flow into or out of each of the four intersections during a certain hour. During that hour, what was the amount of traffic flow along the street from R to S if the total amount of traffic flow into P was 1,200 ? (Assume that none of the traffic originates or terminates in the network.)

A. 200
B. 250
C. 300
D. 350
E. 400


OA B

Source: Official Guide
The total amount of traffic flow into P was 1,200
There are 800 cars heading towards P from the left, which means the remaining 400 cars must be heading towards P from below.
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Since 1200 cars entered intersection P, 1200 cars must leave intersection P.
Since 900 cars are leaving intersection P upwards, the remaining 300 must be leaving intersection P to the right.
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At this point, we can see that there are 800 cars entering intersection Q, which means there must be 800 cars leaving intersection Q.
Since 200 cars are leaving intersection Q to the right, the remaining 600 cars must be leaving intersection Q downwards
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Finally, we can see that there are 1000 cars entering intersection R, which means there must be 1000 cars leaving intersection R.
Since 750 cars are leaving intersection R downwards , the remaining 250 cars must be leaving intersection R to the left,
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Answer: B
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