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  3. [img]2022m10x/ct_ve01204002j_0014_221018[/img]The figure above represents a net

[img]2022m10x/ct_ve01204002j_0014_221018[/img]The figure above represents a net

游客2024-01-13  30
问题
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，)
选项 A、200
B、250
C、300
D、350
E、400
答案 B
解析 In the following, the notation A→B will be used to represent the amount of traffic flow from A into B. Let x represent R→S. From the figure, the amount of traffic flow into P was 800 plus S→P. The total amount of traffic flow into P was 1,200, so S→P was 400. The amount of traffic flow into S was 550 plus R→S, so 550 + x. The amount of traffic flow out of S was 400 plus S→P, or 400 + 400 = 800. Since the amount of traffic flow into S must equal the amount of traffic flow out of S, 550 + x = 800. Therefore, x = 250, so R→S was 250.
The correct answer is B.
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