# 5.1 - Rounding Decimals

The student

• given a decimal through thousandths, will round to the nearest whole number, tenth, or hundredth.

### BIG IDEAS

• So that I will be able to apply rounding when I estimate (i.e I know I have \$50 to spend so I need to round the price of each item first and then add them together to ensure I have enough money)
• So that I can tell the approximate... (time, temperature, number of people attending a function, number of party favors I'll need to have, etc.)
• So that I don't go over budget
• So that I don't over or under prepare for an event (i.e. too many seats, too much food, etc.)

### UNDERSTANDING THE STANDARD

• The structure of the base-ten number system is based upon a simple pattern of tens in which each place is ten times the value of the place to its right. This is known as a ten-to-one place value relationship. To investigate this relationship, use base-ten proportional manipulatives, such as place value mats/charts, decimal squares, base-ten blocks, meter sticks, as well as the ten-to-one non-proportional model, and money.
• A decimal point separates the whole number places from the places less than one. Place values extend infinitely in two directions from a decimal point. A number containing a decimal point is called a decimal number or simply a decimal.
• read the whole number to the left of the decimal point;
• read the decimal point as “and”;
• read the digits to the right of the decimal point just as you would read a whole number; and
• say the name of the place value of the digit in the smallest place.
• Any decimal less than one will include a leading zero (e.g., 0.125).  This number may be read as “zero and one hundred twenty-five thousandths” or as “one hundred twenty-five thousandths.”
• Decimals can be rounded in situations when exact numbers are not needed.  Strategies for rounding whole numbers can be applied to rounding decimals.
• Number lines are tools that can be used in developing a conceptual understanding of rounding decimals.  One strategy includes creating a number line that shows the decimal that is to be rounded.  Locate it on the number line. Next, determine the closest multiples of whole numbers, tenths, or hundredth, it is between. Then, identify to which it is closer.

### ESSENTIALS

The student will use problem solving, mathematical communication, mathematical reasoning, connections, and representations to

• Given a decimal through thousandths, round to the nearest whole number, tenth, or hundredth.

### KEY VOCABULARY

Updated: May 29, 2019