Andrea poured 6 litres of 10% cream into 3 litres of 15% cream. What is the percentage of cream in the final mixture?
let x = percentage of cream in final mixture
6 * 0.1 + 3 * 0.15 = 9x
0.6 + 0.45 = 9x
1.05 = 9x
x = 0.116666666...
which means the percentage is about 11.67%
(tell me if I did something wrong since I haven't done these types of problems in a while)