Pre-Algebra: Chapter 9-10
Percent of Change
We have a simple formula for percent of increase or percent of decrease. We use: (new value – old value) รท (old value) to find the percentage change. If the percent change is NEGATIVE, it is a DECREASE. If the change is POSITIVE, it is an INCREASE.
Here are some good examples from Purplemath.com
Algebra: Chapter 10-8
Mixture Problems
Whether they are acid mixes or coffee bean blends, we treat these problems the same. “x” will stand for the amount of one of the mixes and the (total amount – x) is the amount of the other mix. Convert percentages to decimals (remember D2P?) and use monetary cost per pound as decimals (like $2.04 is represented by 2.04) and you’ll be fine.
The problems CAN be solved with 2 variables, x and y, BUT it requires 2 equations and substitution- I think it is just twice the work of developing one equation with just 1 variable.
Here is a great Purplemath link.