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R.3 - ROUNDING NUMBERS, ESTIMATING ANSWERS AND DISPLAYING INFORMATION R.4 – SUBTRACTION WITH WHOLE NUMBERS Math 081 Catherine Conway Rounding Steps for Rounding Numbers • Locate the digit just to the right of the place you are to round to. • If that digit is less than 5, replace it and all digits to its right with zeros. • If that digit is 5 or greater, replace it and all digits to its right with zeros, and add 1 to the digit to its left. Examples Round 5,482 to the nearest hundred. Add 1 to 4 Change to zeros 5,482 = 5,500 Greater than 5 You Try: pg 28 #42, 43, 46 Pg 28 #42, 43, 46 5,950 6,000 5,900 6,000 6,000 6,000 11,110 11,100 11,000 Practice The pie chart shows how a family of 3 earning $52,402 a year spends their money SPENDING Taxes, 7,248, Miscellaneous, 6,987 Entertainment, 3,278 Car Expenses, 8,413 Food, 6,423 House Payment, 17,904 Savings Account, 2,149, 1. To the nearest ten dollars, what is the total amount spent on food and entertainment? $9,700 2. To the nearest thousand dollars, how much of their income is spent on items other than taxes and savings? $43,000 Estimating • Estimation is used to simplify the problem so that an approximate answer can be found. Example: Estimate the answer to the following problem by rounding to the nearest thousand. 4,621 + 1,687 + 888 + 4,210 Round each number to the nearest thousand 5,000 + 2,000 + 1,000 + 4,000 12,000 You Try: Pg 30 #60, 62 Pg 30 #60, 62 Subtraction with Whole Numbers • Common words/phrases that represent subtraction: • difference, subtract, take away, decrease, fewer, less than, decline, below, minus • See Table 1 on page 33 Best way to Subtract numbers: Align the numbers vertically by place values and subtract in each column. Practice: pg 34 & 35 -Example 1 and 2 Subtraction with Borrowing • Subtraction must involve borrowing when the bottom digit in any column is larger than the digit above it. 83 = 8 tens + 3 ones 35 = 3 tens + 5 ones 83 = 8 tens + 3 ones Borrow - 7 tens + 13 ones Practice: 35 = 3 tens + 5 ones pg 39 # 38, 4 tens + 8 ones = 48 40 Example: 83 – 35 Practice: pg 39 # 38, 40 Correction on the homework •R.3: Question 4 and 9 It says to round to the nearest hundred, but it really wants you to round to the nearest thousand.