Extra: compound proportion
In compound proportion three quantities change together. In the table change one quantity at a time and decide whether each change is direct or inverse.
- Germany: grade 7
- Afghanistan: grade 8
- Palestine: grade 7
- Ukraine: grade 6
- Russia: grade 7
Guide
This extra studio comes from the Afghan Grade 8 lesson on compound proportion. It builds on the proportion table, direct proportion and inverse proportion from the proportion studio.
The method: write a new row of the table for each change, and in each row change only one quantity. Each time ask: if this quantity goes up, does the unknown go up (direct) or down (inverse)?
The last column works itself out and shows what stays the same, such as "chairs per worker per day". If your answer is right, that number is the same in every row.
Common slips: treating every change as direct; applying both changes at once without thinking, or forgetting one of them.