GUIDE深度 · Deep dive
Direct, Inverse and Proportional Sharing
Direct proportion has constant y/x; inverse has constant xy; proportional sharing finds total parts, then one part, then multiplies.
Direct/inverse
Direct: double x, double y.
Inverse: double x, halve y.
Sharing
Total parts = 3+5=8.
One part = total / 8.
Shares = one part x 3 / x 5.
For word problems, write the ratio labels first (red:blue, cost:items) so you do not invert the relationship.
FAQ
How to tell direct from inverse?
Check whether the product or the ratio is constant.
Round shares up?
Usually not in math; only for real indivisible items.