Multiple choice general knowledge math & puzzles

Three traffic lights at crossings change colour after every 50 seconds, 35 seconds and 30 seconds respectively. At a particular time, all the crossing has red colour of light. After what time next, they will again have the red colour?

  1. 950

  2. 900

  3. 1020

  4. 1050

Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The lights will all show red again at the LCM of 50, 35, and 30. Prime factorization: 50 = 2 × 5², 35 = 5 × 7, 30 = 2 × 3 × 5. LCM = 2 × 3 × 5² × 7 = 1050. This means all three lights will simultaneously be red again after 1050 seconds (17 minutes 30 seconds). Option D is correct.