7 Chapter Decimals: Rational Numbers and Percent

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7 Chapter Decimals: Rational Numbers and Percent

7-2 Operations on Decimals
Multiplying Decimals Scientific Notation Dividing Decimals Mental Computation Rounding Decimals Estimating Decimal Computations Using Rounding Round-off Errors Copyright © 2013, 2010, and 2007, Pearson Education, Inc.

Adding Decimals We can change the problem to one we already know how to solve, that is, to a sum involving fractions. Copyright © 2013, 2010, and 2007, Pearson Education, Inc.

Multiplying Decimals If there are n digits to the right of the decimal point in one number and m digits to the right of the decimal point in the second number, multiply the two numbers ignoring the decimals, and then place the decimal point so that there are m + n digits to the right of the decimal point in the product. Copyright © 2013, 2010, and 2007, Pearson Education, Inc.

Example 7-4 Compute each of the following: a. (6.2)(1.43) b. (0.02)(0.013) Copyright © 2013, 2010, and 2007, Pearson Education, Inc.

Example 7-4 (cont) Compute each of the following: c. (1000)(3.6) Copyright © 2013, 2010, and 2007, Pearson Education, Inc.

Scientific Notation Scientists use scientific notation to handle either very large or very small numbers. For example, the distance light travels in one year is 5,872,000,000,000 miles, called a light year, is expressed as · 1012. The mass of an electron, atomic mass units, is expressed as · 10−4. Copyright © 2013, 2010, and 2007, Pearson Education, Inc.

Definition Scientific Notation In scientific notation, a positive number is written as the product of a number greater than or equal to 1 and less than 10 and an integer power of 10. To write a negative number in scientific notation, treat the number as a positive number and adjoin the negative sign in front of the result. Copyright © 2013, 2010, and 2007, Pearson Education, Inc.

Example 7-5 Write each of the following in scientific notation: a. 413,682,000 · 108 b 2.31 · 10−5 c. 83.7 8.37 · 101 d. −10,000,000 −(1 · 107) Copyright © 2013, 2010, and 2007, Pearson Education, Inc.

Example 7-6 Convert each of the following to standard numerals: a · 10−5 b · 107 31,200,000 c. −(4.08 · 104) −40,800 Copyright © 2013, 2010, and 2007, Pearson Education, Inc.

Scientific Notation Calculators with an key can be used to represent numbers in scientific notation. EE For example, to find (5. 2 · 1016) (9.37 · 104), press Copyright © 2013, 2010, and 2007, Pearson Education, Inc.

Dividing Decimals Divide by 4. Copyright © 2013, 2010, and 2007, Pearson Education, Inc.

Dividing Decimals When the divisor is a whole number, the division can be handled as with whole numbers. The decimal point can be placed directly over the decimal point in the dividend. Copyright © 2013, 2010, and 2007, Pearson Education, Inc.

Dividing Decimals When the divisor is not a whole number, as in ÷ 0.32, we can obtain a whole-number divisor by expressing the quotient as a fraction, and then multiplying the numerator and denominator of the fraction by This corresponds to rewriting the problem in form (a) as an equivalent problem in form (b), as follows: Copyright © 2013, 2010, and 2007, Pearson Education, Inc.

Dividing Decimals In elementary school texts, this process is usually described as “moving” the decimal point two places to the right in both the dividend and the divisor. Copyright © 2013, 2010, and 2007, Pearson Education, Inc.

Mental Computation Some tools for doing mental computations with whole numbers can be used for decimal numbers: Breaking and bridging = = = = 9.68 Copyright © 2013, 2010, and 2007, Pearson Education, Inc.

Mental Computation 2. Using compatible numbers Decimal numbers are compatible when their sum is a whole number. 7.91 3.85 4.09 + 0.15 12 + 4 16 Copyright © 2013, 2010, and 2007, Pearson Education, Inc.

Mental Computation 3. Making compatible numbers 9.27 + 3.79 = = = 13.06 4. Balancing with decimals in subtraction 4.63 − 1.97 = = − ( ) = 4.66 = − 2.00 2.66 Copyright © 2013, 2010, and 2007, Pearson Education, Inc.

Mental Computation 5. Balancing with decimals in division Copyright © 2013, 2010, and 2007, Pearson Education, Inc.

Rounding Decimals Rounding can be done on some calculators using the key. FIX To round the number to thousandths, enter FIX 3 The display will show Then enter and press the key. The display will show = Copyright © 2013, 2010, and 2007, Pearson Education, Inc.

Example 7-9 Round each of the following numbers: a to the nearest hundredth 7.46 b to the nearest tenth 7.5 c to the nearest unit 7 d to the nearest thousand 7000 e. 745 to the nearest ten 750 f to the nearest ten 70 Copyright © 2013, 2010, and 2007, Pearson Education, Inc.

Estimating Decimal Computations Using Rounding
Rounded numbers can be useful for estimating answers to computations. When computations are performed with rounded numbers, the results may be significantly different from the actual answer. Other estimation strategies, such as front-end, clustering, and grouping to nice numbers, that were investigated with whole numbers also work with decimals Copyright © 2013, 2010, and 2007, Pearson Education, Inc.