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

Question

https://gmatclub.com/forum/download/file.php?id=50459 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 PS03502.01 2019-09-21_1647.png

ScottTargetTestPrep · Accepted Answer

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

CareerGeek · Answer

Let the traffic from S to P = y
& traffic from R to S = x

Traffic flow into P = 1200
--> 800 + y = 1200
--> y = 400

Net Traffic inflow at S = Net Traffic out flow
--> x + 550 = 400 + y
--> x + 550 = 800
--> x = 250

IMO Option B

Archit3110 · Answer

distance from R to S = y
distance from S to P = x
given at P = 1200
1200=x+800
x=400
550+y= 400+x ; x=400
550+y=800
y=250
IMO B

Xemo · Answer

Can we do it this way? Moving from P to point Q calculating inflows and outflows
1200 - 900 = 300
300 + 500 - 200 = 600 (point Q)
600 - 350 (point R net inflows and outflows) = 250

chetan2u · Answer

Pritishd · Answer

The image attached with this post provides insight into the approach.

1. We are given that the flow at P was 1,200. Now, 800 of these are coming from left of P and hence we can safely say that 400 (shown in green) are coming from the bottom of P
2. Now, 900 out of these 1,200 have to move out from the top, hence the 300 (shown in green) move towards Q
3. At Q, a traffic of 800 flows in. And 200 out of these 800 have to flow out through the right of Q, hence the remaining 600 moves towards R
4. At R, a traffic of 1,000 flows in. And 750 out of these 1,000 flow out through the bottom road of R,hence the remaining 250 move towards S

Ans.  B

reynaldreni · Answer

Let us start from P, remember Total Inflow = Total Outflow.  
 At Intersection P, 
P-Total Inflow = 1200  , We know From Outside = 800, so From S to P = 400.
P-Total Outflow = 1200  , We know To Outside=900, so From P to Q= 300.
 
 At Intersection Q,
Q-Total Inflow =   = 500 + 300 = 800
Q-Total Outflow = 800   = 200 +To R = 800, so We get, From Q to R = 600

At Intersection R,
R-Total Inflow =   = 400 + 600 = 1000
R-Total Outflow = 1000   = 750 + To S, so We get, From R to S = 250

OA B

Fdambro294 · Answer

(1st Junction) 1,200 cars going INTO Point P

If 1,200 must go into P there are ONLY 2 Places via which the roads feed into Point P

either:

directly to the LEFT of Point P = 800

or

from Point S ------> Point P = ?
___________________________

Therefore, we know that on the street: Point S ---->Point P : there must be 400

(2nd Junction) 1,200 cars Coming OUT of Point P

When you come out of Point P, there are only 2 Ways you can travel:

either:

directly North of Point P = 900

or

to the Right from Point P -----> Point Q = ??
____________________________________

since all 1,200 cars that went into Point P must be accounted for, we know that on:

Street P -------> Q ........there must be 300 cars

(3rd) Cars feeding into Point Q

The TOTAL Number of Cars that Feed into Point Q is =

(300 Cars from P ----->Q) + (500 Cars coming Directly North of Q) = 800 Cars driving into Q

From these 800 cars that go into Q ---------> 200 Cars exit Q to the Right

Therefore, since there is only 1 Other Way to Exit Q, the remaining 600 Cars must be traveling on:

Q -------->R ......600 Cars

(4th) Cars feeding into Point R

there are 2 Points via which the cars feed into Point R

Q ----->R ......600 cars

OR

Directly to the Right of Point R = 400 cars
___________________________________
Total of 1,000 Cars feed into Point R

Finally, since there are ONLY 2 Exits out of Point R:

750 of these 1,000 Cars drive directly South from Point R

and

the Remaining 250 Cars must be Driving from Point R -----> Point S

This is the Answer: there are 250 Cars on the Street from Point R ------>Point S

-B-

Basshead · Answer

Given:   Traffic flow into P was 1,200

900 flows out of P. Therefore 300 flows east to Q.

Q = 300 (from P) + 500 = 800 - 200 (flows east) = 600 flowing down to R

R = 600 + 400 = 1,000 - 750 (flows south) = 250

240 flows from R to S.

Answer is B.

zoezhuyan · Answer

dear ,  ScottTargetTestPrep 
how can I get the total flow of S is zero, how can I get that total flow into S equals to total flow out S.

would you please help ?

ScottTargetTestPrep · Answer

Response:
 
We conclude that must be the case from the note “Assume that none of the traffic originates or terminates in the network.” For instance, if the total flow into S was 200 but the total flow out of S was 150, it would mean that 50 cars remained in intersection S, i.e. 50 cars terminated in S. Conversely, if the total flow into S was 150 but the total flow out of S was 250, then it would mean that 100 cars originated from the intersection S. Since neither can be true, it must be true that the total flow into each intersection is equal to the total flow out of each intersection.

BrentGMATPrepNow · Answer

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. 
 https://i.imgur.com/n444kbn.png

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. 
 https://i.imgur.com/HCRvMbz.png

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
 https://i.imgur.com/39klB3U.png

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,
 https://i.imgur.com/fvVx4PK.png

Answer: B

MBAHOUSE · Answer

It’s the kind of question that you don’t bring any math concept to it. You need to decide in real time what to do and how to do. At the GMAT to gain 700+ you need to get right 90% of the easy questions, 80% of the medium questions and 65% of the hard question. Don’t loose your entire test trying to kill at any cost hard questions. Guess and go forward eventually.

Attachments

9FB4C1BE-11EC-437C-9739-23D4033C3841.jpeg [ 472.69 KiB | Viewed 20818 times ]

KarishmaB · Answer

Here are the steps: Since incoming traffic at P is 1200, it means traffic coming in from S to P is 400 (since 800 is coming in from the other leg). Outgoing traffic from P must also be 1200 and since 900 goes in one leg, 300 must be going to Q. Following the same process for points Q and R too, we get that traffic in the RS lane must be 250.

Attachment:

Screenshot 2023-08-25 at 11.15.13 AM.png [ 100.47 KiB | Viewed 13945 times ]

Answer (B)

soniasw16 · Answer

Can someone share if such questions are part of the GMAT FE?

Bunuel · Answer

This question is from an older Official Guide, which means it’s a retired real exam question. There’s no reason it couldn’t still appear today, it doesn’t involve geometry and remains fully relevant to the GMAT Focus Edition syllabus.

KarishmaB · Answer

I would say they are even more relevant in FE than Classic. A puzzle kind of network graph using reasoning is certainly FE's style.

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

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