Pre-Test
Post-Test
Math Lesson 7
Using Very Small and Very Large Numbers
Pre-Test |
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Post-Test |
Instruction 7-1
Estimate, Round Off, and Manipulate Very Small and Very Large Numbers | Percents and Their Interpretations | Positive Integer Powers of Non-negative Integers | Decimals, Fractions, Mixed Numbers, and Positive and Negative Integers on the Number Line | Summary
ESTIMATE, ROUND OFF, AND MANIPULATE VERY SMALL AND VERY LARGE NUMBERS
CA GR5 NS 1.1., CA GR7 MR 2.1
Rounding Off Numbers
To round off a number, use place-value to round decimals and whole numbers.
To round to the nearest number use place-value. Look at the digit in the place to the right of where you want to round. Determine whether the digit is greater than 5 or less than 5. Round appropriately.
Example 1 Round 234.423 to the nearest tenth.
| Look at the digit in the hundredth place. | 234.423 | |
| Compare the digit to 5. | 2 < 5, round down | |
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If it is less than 5, round down If it is more than 5, round up |
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| Answer: | 234.4 | |
Example 2 Round 4,278.43 to the nearest hundred.
| Look at the digit in the tens place. | 4,278.43 | |
| Compare the digit to 5. | 7 > 5, round up | |
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If it is less than 5, round down If it is more than 5, round up |
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| Answer: | 4,300 | |
Estimating
Estimation is a process for determining an answer that is close to the actual total. Estimation can be used in addition, subtraction, division, and multiplication. Estimation makes use of rounded off numbers. The easiest way to find the total of an answer, use the values of the “front” digits and then adjust the estimate by grouping the remaining digits, this is also called front-end estimation.
Example 1 Estimate the sum of 347 + 874.
| Use front-end estimation. |
347 874 |
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| Compare the digit to 5. |
4 < 5, round down 7 > 5, round up |
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If it is less than 5, round down If it is more than 5, round up |
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| Find the sum of the estimated numbers. | 300 + 900 = 1,200 | |
Example 2 Estimate the difference of 8,329 – 3,782 to the nearest hundred place.
| Round off the numbers to the nearest hundred place. |
8,329 3,782 |
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| Compare the digit to 5. |
2 < 5, round down 8 > 5, round up |
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If it is less than 5, round down If it is more than 5, round up |
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| Find the difference of the estimated numbers. | 8,300 – 3,800 = 4,500 | |
Example 3 Estimate the product of 32 x 46
| Round off the two numbers. |
32 46 |
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| Compare the digit to 5. |
2 < 5, round down 6 > 5, round up |
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If it is less than 5, round down If it is more than 5, round up |
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| Find the product of the estimated numbers. | 30 x 50 = 1,500 | |
Example 4 Estimate the quotient of 654 ÷ 13
| Round the numbers. |
654 13 |
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| Compare the digit to 5. |
5 = 5, round up 3 < 5, round down |
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If it is less than 5, round down If it is more than 5, round up |
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| Find the quotient of the estimated numbers. | 700 ÷ 10 = 70 | |
Worksheet 1 Round off to the Nearest Tenth.
Worksheet 2 Round off to the Nearest Hundredth.
Worksheet 3 Round off to the Nearest Thousandth.
Worksheet 4 Round off to the Nearest Ten Thousandth.
Worksheet 5 Round off to the Nearest Ten
Worksheet 6 Round off to the Nearest Hundred
Worksheet 7 Round off to the Nearest Thousand
Worksheet 8 Round off and Multiply
Worksheet 10 Round off and Subtract
Worksheet 11 Round off and Divide
Links for Students, Parents and Teachers
Now let's do Practice Exercise 7-1 (top).
Next Page: Percents and Their Interpretations (top)