Ratios and percentage

[Kerrieyarwood83]

Hi, I've had many attempts at these and and fail Everytime. I need help with these..
Qn1: Green paint needs to be mixed with white paint to get the correct shade. The instructions say mix the green and white to a 1:3 ratio. Using 500ml of green, how much white paint will be needed in ml?

Qn2: If the amount of green paint was halved, how much white paint would be needed?

Qn3: A set design needs to be fitted with tiles to the proportion of 4 white to 3 black. How many black tiles will be needed to go with 12 white ones? I worked this out to be 9 black tiles but the next an asks what is the percentage of black tiles used?

 

[JeffM]

We seldom give answers because then you are unsure of how to apply that answer to different cases.

Here is the idea behind ratios expressed like 1:3. They ignore the total and focus just on the parts.

So in the first question, 1:3 means that the white paint will be three times the green paint, whatever the green paint may be.

So what is the amount of white paint needed in question 1? Extra question, how much paint will you have in total?

Percentage shows the part relative to the total. We divide the part by the total and multiply the result by 100. So sticking with the first question, when the mixing is done what percentage consists of green paint?