Question

There is a traffic light at the intersection of Walnut Street and Lawrence Avenue. The traffic light on Walnut Street follows a cycle. It is green for 50 seconds, yellow for 10 seconds, and red for 30 seconds. As you travel along Walnut and approach the intersection, what is the probability that the first color you see is red?
1/5

1/3

3/5

1/2

Answer 1

From the given above, we calculate for the total cycle time by adding up all the durations given for the yellow light, red light, and green. That is,
    total time = 30 s + 10 s + 50 s = 90s
Hence, the total time is equal to 90 s. From this, we calculate for the probability that the first light that will be seen is a red light by dividing the duration of the red light in the cycle by the total time. 
 Probability = (30 seconds) / (90 seconds) 
                   = 1/3

Therefore, the probability that the red light will be seen first is equal to 1/3. The answer is second choice.