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At a traffic light, one cycle through green-yellow-red lasts for 84 seconds. The green light is on seven times longer than the yellow light, and the red light is on thirteen times longer than the yellow light. For how long is each colored light on during one cycle?

Answer 1

let t be the seconds for yellow light, so green light is on 7t, red light is on 13t.

 

on cycle total 84 = 7t + t + 13t = 21t

so t = 4

 

so yellow light on 4 sec, green light on 7t = 28 sec, red light on 13t = 52 sec