Estimating Products Using Rounding
Estimating Products Using Rounding (Chapter 4) is a Grade 4 math skill in enVision Mathematics, Chapter 4: Use Strategies and Properties to Multiply by 2-Digit Numbers. Students round 2-digit factors to the nearest ten before multiplying to estimate products.
Key Concepts
Property To estimate the product of two numbers, round one or both factors to a nearby place value (like the nearest ten or hundred) to make the multiplication easier to perform mentally. The symbol $\approx$ means "approximately equal to".
Examples To estimate $48 \times 72$, round $48$ to the nearest ten, which is $50$. Then, calculate $50 \times 70 = 3500$. So, $48 \times 72 \approx 3500$.
To estimate $32 \times 88$, round $32$ down to $30$ and round $88$ up to $90$. Then, calculate $30 \times 90 = 2700$. So, $32 \times 88 \approx 2700$.
Common Questions
How do you estimate 2-digit products using rounding?
Round each 2-digit factor to the nearest ten, then multiply the rounded numbers. The product gives a reasonable estimate of the actual answer.
What is an example of estimating a 2-digit product by rounding?
To estimate 43 times 67, round to 40 times 70 equals 2,800. The exact answer of 2,881 is close to this estimate.
When should you round both factors vs just one?
Rounding both factors gives a quicker estimate. Rounding only one factor that is far from a friendly number while keeping the other exact can give a more accurate estimate.
How does rounding help with 2-digit multiplication?
Rounding to tens makes the mental multiplication much simpler since multiplying multiples of 10 only requires the basic fact and annexing zeros.
What chapter in enVision Grade 4 covers rounding estimation for 2-digit multiplication?
Estimating products using rounding is covered in Chapter 4: Use Strategies and Properties to Multiply by 2-Digit Numbers in enVision Mathematics Grade 4.