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Chapter 7

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  1. Chapter 7 Section 7.1 Place Systems

  2. Base-Ten Place-Value System The sleek efficient number system we know today is called the base-ten number system or Hindu-Arabic system. It was first developed by the Hindus and Arabs. This used the best features from several of the systems we mentioned before. 1. A limited set of symbols (digits). This system uses only the 10 symbols:0,1,2,3,4,5,6,7,8,9. 2. Place Value. This system uses the meaning of the place values to be powers of 10. For example the number 6374 can be broken down (decomposed) as follows: The last row would be called the base-tenexpanded notation of the number 6374.

  3. Write each of the numbers below in expanded notation. • a) 82,305 • = 810,000 + 21,000 + 3100 + 010 + 51 • = 8104 + 2103 + 3102 + 5100 • b) 37.924 • = 310 + 71 + 9(1/10) + 2(1/100) + 4(1/1000) • = 3101 + 7100 + 910-1 + 210-2 + 410-3 • Write each of the numbers below in standard notation. • a) 6105 + 1102 + 4101 + 5100 • = 600,000 + 100 + 40 + 5 • = 600,145 • b) 7103 + 3100 + 210-2 + 810-3 • = 7000 + 3 + .02 + .008 • = 7003.028

  4. Writing Numbers in Other Bases A number in another base is written using only the digits for that base. The base is written as a subscripted word after it (except base 10). For Example: 10324 is a legitimate base four number “Read 1-0-3-2 base four” 15424 is not a legitimate base four number not allowed 4 or 5

  5. Place Values The place values for each number in a different base start with the ones place as the right most digit and go up by the next higher power of the base as you move to the left. Example: What is the place value of the digit 2 in each of numbers below? 175268 2035 21103 32104 734629 The digit 2 is in the 81 = 8’s place The digit 2 is in the 52 = 25’s place The digit 2 is in the 33 = 27’s place The digit 2 is in the 42 = 16’s place The digit 2 is in the 90 = 1’s place Counting The next slide shows the first 17 base four numbers along with what they are in base 10 and how they are represented with base four Dienes Blocks.

  6. Notice that the numbers in go in order just like in base 10 but only using the symbols 0, 1, 2, 3. In base 4 numbers are grouped in blocks 1, 4, 16, ….

  7. We can use this different number system to illustrate what it is like to try to learn to count. Give the three numbers that come before and the three numbers that come after each of the numbers below. 23675 2105 12334 111 Notice that when the numbers convert they stay in the same order. 23676 2115 13004 112 23677 2125 13014 113 23679 2145 13034 115 23680 2205 13104 116 23681 2215 13114 117 Converting a number to base 10 This process is a combination of multiplication and addition. You multiply each digit by its place value and add up the results. Convert 13024 to base 10. In expanded form this number is given by: 13024 = 1×43 + 3×42 + 0×41 + 2×40 13024

  8. Lets convert some of these other numbers to base 10. 20123 2748 2748 = 2×82 + 7×81 + 4×80 20123 = 2×33 + 0×32 + 1×31 +2×30 Converting a number to a different base To convert a number from base 10 to a different base you keep dividing by the base keeping tract of the quotients and remainders then reversing the remainders you got. The examples to the right first show how to convert a base 10 number 2467 to base 10. Then how you convert 59 to base three. (Notice 59 agrees with what we got for the base three number above. remainders remainders quotients quotients 593 = 19 r 2 193 = 6 r 1 63 = 2 r 0 23 = 0 r 2 246710 = 246 r 7 24610 = 24 r 6 2410 = 2 r 4 210 = 0 r 2 2467 20123

  9. Base Two The important details about base 2 are that the symbols that you use are 0 and 1. The place values in base 2 are (going from smallest to largest): 20 (1) 210 (1024) 29 (512) 28 (256) 27 (128) 26 (64) 25 (32) 24 (16) 23 (8) 22 (4) 21 (2) Change the base 2 number 1100112 to a base 10 (decimal) number. Change the base 10 (decimal) number 47 to a base 2 (binary) number. 47  2 = 23 remainder 1 23  2 = 11 remainder 1 11  2 = 5 remainder 1 5  2 = 2 remainder 1 2  2 = 1 remainder 0 1  2 = 0 remainder 1 1100112 11 = 1 12 = 2 04 = 0 08 = 0 116 = 16 132 = 32 51 47 = 1011112

  10. Base 12 and 16 For bases that are larger than 10 we need to use a single symbol to stand for the "digits" in a number that represent more than 10. This is because if you use more than one symbol the place values will get off. In particular, bases 12 and 16 are sometimes very useful. In base 12 the digit 10 is represented with a letter T and the digit 11 is represent with a letter E. In base 16 the letters A, B, C, D, E, F represent the digits 10, 11, 12, 13, 14, 15 respectively. T3E12 E1 = 11 1 = 11 312 = 3 12 = 36 T144 = 10144 = 1440 1477 Convert T3E12 to base 10.

  11. Write the base 16 number A2D16 in expanded form and convert it to base ten. A2D16 In expanded form A2D16 is: A×162 + 2×161 + D×160 10×162 + 2×161 + 13×160 D1 = 13 1 = 13 216 = 2 16 = 32 A256 = 10256 = 2560 2605 Converting from Base to Base If we wish to convert from one strange base to another we do this by "going through" base ten. In other words, for example if we want to convert from base 5 to base 16, first convert base 5 to base ten then convert that base ten number to base 16. Example, Convert 32045 to base 16. 1st convert 32045 to base 10 2nd convert 429 to base 16 32045 429  16 = 26 remainder 13 = D 26  16 = 1 remainder 10 = A 1  16 = 0 remainder 1 = 1 4×1 = 4 0×5 = 0 2×25 = 50 3×125 = 375 429 We get the following: 32045 = 1AD16