Answer :
- Round each number in the expressions to the nearest whole number.
- Calculate the estimated product for each expression.
- Compare the estimated products with 45.
- The expression with an estimated product of 45 is $\boxed{8.7 \times 5.28}$.
### Explanation
1. Problem Analysis
We are given four multiplication expressions and asked to identify the one with an estimated product of 45. To do this, we will estimate the product of each expression by rounding the numbers to the nearest whole number or a number that is easy to multiply.
2. Estimating Products
Let's estimate the product of each expression:
1. $44.7 \\times 2.1$: Round $44.7$ to $45$ and $2.1$ to $2$. Estimated product: $45 \\times 2 = 90$.
2. $75 \\times 8.4$: Keep $75$ as is and round $8.4$ to $8$. Estimated product: $75 \\times 8 = 600$.
3. $8.7 \\times 5.28$: Round $8.7$ to $9$ and $5.28$ to $5$. Estimated product: $9 \\times 5 = 45$.
4. $38.1 \\times 7.3$: Round $38.1$ to $40$ and $7.3$ to $7$. Estimated product: $40 \\times 7 = 280$.
3. Identifying the Correct Expression
Comparing the estimated products, we see that the expression $8.7 \\times 5.28$ has an estimated product of 45.
4. Final Answer
Therefore, the expression with an estimated product of 45 is $8.7 \\times 5.28$.
### Examples
Estimating products is useful in everyday situations, such as when you're grocery shopping and want to quickly calculate the total cost of your items. By rounding the prices and quantities, you can get a rough estimate of the total amount you'll need to pay, helping you stay within your budget. This skill is also helpful in quickly assessing whether you have enough money to make a purchase or comparing prices between different stores.
- Calculate the estimated product for each expression.
- Compare the estimated products with 45.
- The expression with an estimated product of 45 is $\boxed{8.7 \times 5.28}$.
### Explanation
1. Problem Analysis
We are given four multiplication expressions and asked to identify the one with an estimated product of 45. To do this, we will estimate the product of each expression by rounding the numbers to the nearest whole number or a number that is easy to multiply.
2. Estimating Products
Let's estimate the product of each expression:
1. $44.7 \\times 2.1$: Round $44.7$ to $45$ and $2.1$ to $2$. Estimated product: $45 \\times 2 = 90$.
2. $75 \\times 8.4$: Keep $75$ as is and round $8.4$ to $8$. Estimated product: $75 \\times 8 = 600$.
3. $8.7 \\times 5.28$: Round $8.7$ to $9$ and $5.28$ to $5$. Estimated product: $9 \\times 5 = 45$.
4. $38.1 \\times 7.3$: Round $38.1$ to $40$ and $7.3$ to $7$. Estimated product: $40 \\times 7 = 280$.
3. Identifying the Correct Expression
Comparing the estimated products, we see that the expression $8.7 \\times 5.28$ has an estimated product of 45.
4. Final Answer
Therefore, the expression with an estimated product of 45 is $8.7 \\times 5.28$.
### Examples
Estimating products is useful in everyday situations, such as when you're grocery shopping and want to quickly calculate the total cost of your items. By rounding the prices and quantities, you can get a rough estimate of the total amount you'll need to pay, helping you stay within your budget. This skill is also helpful in quickly assessing whether you have enough money to make a purchase or comparing prices between different stores.
