Use the two models to compare \(\frac{4}{5}\times20\) and \(\frac{5}{4}\times20\). In model a), the selected part lies within the original \(20\). In model b), the left block is the original \(20\) and the rightmost column is the additional fourth-group. Explain how each fraction changes the original amount, then find both products.

Hints
- In each model, identify how many equal groups make one original whole amount.
- Use the numerator to decide how many equal-sized groups are selected.
- Compare each multiplier with \(1\) and compare the selected region with the original amount.
Solution
1. In model a), \(20\) is split into \(5\) equal groups of \(4\), and \(4\) groups are selected. Thus \(\frac{4}{5}\times20=16\).
2. In model b), \(20\) is split into \(4\) equal groups of \(5\), and the model extends to a fifth group. Thus \(\frac{5}{4}\times20=25\).
3. The first multiplier is less than \(1\), so it shrinks the amount. The second is greater than \(1\), so it enlarges the amount.
Answer
\(\frac{4}{5}\times20=16\), which is less than \(20\). \(\frac{5}{4}\times20=25\), which is greater than \(20\).