Question: To find 4 times any number, Susan uses the double double strategy (multiply by 2, then by 2 again). Susan wrote (2 x 9) x 2 to record how she would solve 4 x 9
1. **State the problem:** We want to find 4 times 9 using Susan's double double strategy.
2. **Explain the strategy:** Susan multiplies the number by 2, then multiplies the result by 2 again. This is equivalent to multiplying by 4 because $$4 = 2 \times 2$$.
3. **Write the expression:** Susan wrote $$(2 \times 9) \times 2$$ to represent $4 \times 9$.
4. **Calculate step-by-step:**
- First multiply 2 by 9:
$$2 \times 9 = 18$$
- Then multiply the result by 2:
$$18 \times 2 = 36$$
5. **Verify the result:**
- Direct multiplication:
$$4 \times 9 = 36$$
6. **Conclusion:** Susan's double double strategy correctly calculates $4 \times 9$ as 36.