5100455
Sarah has a supply of sugar. She uses \(\frac{4}{9}\) of the original amount, then later uses \(\frac{7}{10}\) of what remained. What fraction of the original amount is left? Explain how an area model represents the fraction-of-a-fraction multiplication.
Hints
- First find the fraction of the original amount left after the first use.
- What fraction of that remainder is left after \(\frac{7}{10}\) is used?
- In an area model, the overlap represents a fraction of a fraction.
Solution
1. After the first use, \(1-\frac{4}{9}=\frac{5}{9}\) of the original sugar remains.
2. After the second use, \(\frac{3}{10}\) of that remaining amount is left.
3. In an area model, one dimension represents \(\frac{5}{9}\) of the original amount and the other represents keeping \(\frac{3}{10}\) of that part. The overlap represents \(\frac{5}{9}\times\frac{3}{10}=\frac{15}{90}=\frac{1}{6}\) of the original amount.
Answer
\(\frac{1}{6}\) of the original amount is left. In an area model, the overlap of \(\frac{5}{9}\) in one direction and \(\frac{3}{10}\) in the other represents this fraction of the original amount.
