When using a 1% cream and a 6% cream to produce a 4% cream, how many parts of each initial ingredient will be needed?
1%........4%.........6%
|...3.....|.....2....|
An easy way to see this which I learned from Mathmate. So you take 2 parts of the 1% and 3 parts of the 6% to make 4%.
So for 100 g you take 40g of the 1% and 60g of the 6% to make 100 g of 4%.