R.3 - ROUNDING NUMBERS, ESTIMATING ANSWERS AND DISPLAYING INFORMATION

R.4 – SUBTRACTION WITH WHOLE NUMBERS

Math 081Catherine Conway

RoundingSteps 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.

ExamplesRound 5,482 to the nearest hundred.

5,482

= 5,500Greater than 5

Add 1 to 4 Change to zeros

You Try: pg 28 #42, 43, 46

Pg 28 #42, 43, 46

5,950

5,900

6,0006,00

06,000

6,000

11,110

11,100

11,000

Practice

Food, 6423

House Payment, 17904

Savings Account, 2149,

Car Expenses, 8413

Entertainment, 3278

Miscellaneous, 6987

Taxes, 7248,

Spending The pie chart shows how a family of 3 earning $52,402 a year spends their money

1. To the nearest ten dollars, what is the total amount spent on food and entertainment?

2. To the nearest thousand dollars, how much of their income is spent on items other than taxes and savings?

$9,700

$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

5,000 + 2,000 + 1,000 + 4,000

Round each number to the nearest thousand

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.

Example: 83 – 35 83 = 8 tens + 3 ones 35 = 3 tens + 5 ones

Borrow - 7 tens + 13 ones 83 = 8 tens + 3 ones

35 = 3 tens + 5 ones4 tens + 8 ones = 48

Practice: pg 39 # 38, 40

Practice: pg 39 # 38, 40

Correction on the homework

•R.3: Question 4 and 9It says to round to the nearest hundred, but it really wants you to round to the nearest thousand.