Estimating Sums and Differences with Whole Numbers Why

Estimating Sums and Differences with Whole Numbers

Why do we estimate?

When do we estimate?

There are several ways to estimate.

1. Rounding • Rounding makes numbers that are easier to work with in your head. • Rounded numbers are only approximate. • An exact answer generally can not be obtained using rounded numbers. • Use rounding to get a answer that is close but that does not have to be exact.

1. Rounding • Find the number in its spot. Go next door and see what you've got. 5 or more raise the score, 4 or less let it rest. All the numbers to the right run to zero in a fright. 6, 403, 581

1. Rounding • Some problems will tell you what place to round to. • Round to the nearest thousand. 126, 965 193, 210 • When adding or subtracting, round to the highest place value of each number 126, 965+193, 210=_____ estimate http: //www. funbrain. com/tens/index. html

2. Front End Estimation • Front end estimation mostly produces a closer estimate of sums or differences than the answer produced by adding or subtracting rounded numbers.

2. Front End Estimation 1. Look at your math problem. 2. Do both numbers have the same amount of digits? 3. 5, 467+326=______ 4. The number with the least amount of digits sets where you would estimate. 5. Change all numbers behind that number to 0. http: //superteacherworksheets. com/addition/a ddition-3 dig. pdf

3. Compatible Numbers • Compatible numbers for addition and subtraction are numbers that go together easily to make nice numbers.

3. Compatible Numbers • Find numbers that work well together. • Tina has 6 tomatoes, Miriam has 2 tomatoes and Liam has 3 tomatoes. They use 9 tomatoes for a salad. How many tomatoes are left?

3. Compatible Numbers • • 5 + 2 + 5 – 10 9 + 5 +1 – 6 8 + 2 + 7 – 9 4 + 5 – 9 3 + 5 – 8 4 + 6 + 4 + 3 – 7 4 + 2 + 5 – 9 8 + 5 + 2 – 7