Question

A complete cycle of a traffic light takes $60$ seconds. During each cycle the light is green for $25$ seconds, yellow for $5$ seconds, and red for $30$ seconds. At a randomly chosen time, what is the probability that the light will NOT be green?

$\dfrac{1}{4}$

$\dfrac{1}{3}$

$\dfrac{5}{12}$

$\dfrac{1}{2}$

$\dfrac{7}{12}$

Answer: E

Concepts:geometric probability complementary probability

Difficulty rating: 980

Solution:

During a given cycle, the light is not green for $30 + 5 = 35$ seconds.

Then the probability that it is not green is $\dfrac{35}{60} = \dfrac{7}{12}.$

Thus, E is the correct answer.

1999 AMC 8 Problem 10

Answer: E

Difficulty rating: 980

Solution:

Problem 10 in Other Years