Math--Chapter 27

Chapter 27: Add and Subtract Decimals

Lesson 1: Round Decimals. Objective: To round decimals using rounding rules and number lines.

Lesson 2: Estimate Decimals Sums and Differences. Objective: To estimate decimal sums and differences.

Lesson 3: Add Decimals. Objective: To write sums of decimals.

Lesson 4: Subtract Decimals. Objective: To write differences of decimals.

Lesson 5: Add and Subtract Decimals and Money. Objective: To cwrite sums and differences of decimals and money.

Lesson 6: Problem Solving Strategy: Evaluate Reasonableness of Answers. Objective: To use the problem solving strategy evaluate reasonableness of answers.


Vocabulary: tenth, hundredth, decimal, digit, round, number line, decimal point, regrouping, equivalent decimals

tenth: one of ten equal parts

hundredth: one of one hundred equal parts

decimal: a number with one or more digits to the right of a decimal point

digit: any one of ten symbols 0, 1, 2, 3, 4, 5, 6, 7, 8, or 9 used to write numbers

round: replace a number with a number that tells about how many or how much

number line: a line with equally spaced marks named by numbers

mixed number: an amount written as a whole number and a fraction

decimal point: the mark in a decimal number that separates the ones and the tenths place

regrouping: exchanging amounts of equal value when renaming a number

equivalent decimals: two or more decimals that name the same amount


Rounding Help:

Rounding Rap

Mark the place. Look to the right. 4 or less are out of sight. 5 and up will buy one more before they too are out the door. In those empty right-hand spaces, zeros keep the proper places.

Estimating and rounding:

Rounding Whole Numbers:


Our textbook website:


Some good practice websites: