R.3-Estimating, R.4

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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.

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