How to find the ratio

Question

On their way to work Andrew passes 15 traffic lights and Pauline passes 10set of traffic lights. One morning Andrew was stopped by 12 red traffic lights. How many green traffic lights would Pauline need to pass through to have equivalent ratio of red to green traffic lights as Andrew

Answer 1

Andrew red to green ratio = 12:3 = 4:1

because 12 were red so 3 were green

 

Pauline to Andrew: x:(10-x) = 4:1

x(1) = 4(10-x)

x = 40 - 4x

5x = 40

x = 8

 

Pauline red to green ratio: 8:2

 

2 green lights, 8 red lights