Rounding

1
Rounding

• Objective
• Round two-digit numbers to the nearest ten.
• Round three-digit numbers to the nearest hundred.
• Estimate sums and differences.

2
Rounding two-digit numbersRedondeando números de
dos digitos
Two-digit number will be rounded to the nearest
ten.
RULES FOR ROUNDING

1. Underline the number in the place value you will
   round.

2. Look at the number to the right of the
underlined number.

1. If the number to the right is 0, 1, 2, 3, or 4,
   then the underlined number stays the same.

• 26

3
0

1. If the number to the right is 5, 6, 7, 8, or 9,
   then the underlined number needs to go up one
   more number.

So we can say that the number 26 is closer to 30
than to 20.

1. Every number to the right of the underlined
   number becomes a zero.

3
Rounding three-digit numbersRedondeando números
de tres digitos
Three-digit number will be rounded to the nearest
hundred.
RULES FOR ROUNDING

1. Underline the number in the place value you will
   round.

2. Look at the number to the right of the
underlined number.

1. If the number to the right is 0, 1, 2, 3, or 4,
   then the underlined number stays the same.

5
0
0

• 520

1. If the number to the right is 5, 6, 7, 8, or 9,
   then the underlined number needs to go up one
   more number.

So we can say that the number 520 is closer to
500 than to 600.

1. Every number to the right of the underlined
   number becomes a zero.

4
26 is closer to 30 than to 20.
20
26
30
520 is closer to 500 than to 600.
520
600
500
5
Estimating sums
First, round all the numbers using the RULES FOR
ROUNDING Then, perform the operations.
10 10 -------
20
12 8 -------
6
Estimating differences
First, round all the numbers using the RULES FOR
ROUNDING Then, perform the operations.
30 - 10 -------
20
25 - 11 -------
7
RULES FOR ROUNDING

• Underline the number in the place value you will
  round.
• 2. Look at the number to the right of the
  underlined number.
• If the number to the right is 0, 1, 2, 3, or 4,
  then the underlined number stays the same.
• If the number to the right is 5, 6, 7, 8, or 9,
  then the underlined number needs to go up one
  more number.
• Every number to the right of the underlined
  number becomes a zero.

8
Now you practice. Round these numbers.

• 25
• 78
• 36
• 158
• 689
• 324

30 80 40 200 700 300
9
Practice rounding sums and differences
25 - 15 -------
30 - 20 -------
12 36 -------
10 40 -------
128 42 -------
100 40 -------
10
TAKS Preparation Sample Questions
11
The cafeteria is selling ice cream cones for 23
and ice cream sandwiches for 48. If Ms.
Rodriguez buys an ice cream cone and an ice cream
sandwich, about how much money will she spend?

• 1.00
• 70
• 50
• 25