40 green cars 20 silver if same # of green stayed the same how many more silver would need to be added so the ratio of green to silver is 1: 3

So, there will be 40 green cars. if we want the ratio to be 1:3, we will need there to b three times as many silver cars as green cars: 40*3=120.

we already have 20 silver, so we need to add 120-20, that is 100 silver cars!