Decimal Addition and Subtraction — Answer Key
Part A: Fix the Sentence
Each sentence has an error. Rewrite it correctly on the line.
1. Fix the sentence:
0.25 + 0.30 = 0.5
Corrected: 0.25 + 0.30 = 0.55
Grade 4 students align decimals: 5 hundredths + 0 hundredths = 5 hundredths, and 2 tenths + 3 tenths = 5 tenths, giving 0.55.
2. Fix the sentence:
0.75 - 0.40 = 0.45
Corrected: 0.75 - 0.40 = 0.35
Grade 4 learners line up the decimals, subtract 4 tenths from 7 tenths to get 3 tenths, and keep 5 hundredths, giving 0.35.
3. Fix the sentence:
0.42 + 0.15 = 0.67
Corrected: 0.42 + 0.15 = 0.57
Grade 4 students add 2 + 5 = 7 hundredths and 4 + 1 = 5 tenths, giving 0.57, not 0.67.
Part B: Fill in the Blank
Write the missing word or number on each line.
1. 0.45 + 0.30 = 0.75
Grade 4 students align decimals: 5 + 0 = 5 hundredths and 4 + 3 = 7 tenths, giving 0.75.
2. 0.85 - 0.20 = 0.65
Grade 4 learners line up decimals: 5 - 0 = 5 hundredths, 8 - 2 = 6 tenths, so the answer is 0.65.
3. 0.16 + 0.23 = 0.39
Grade 4 students add 6 + 3 = 9 hundredths and 1 + 2 = 3 tenths, giving 0.39.
4. 0.92 - 0.51 = 0.41
Grade 4 learners align decimals and subtract 1 hundredth from 2 hundredths and 5 tenths from 9 tenths, giving 0.41.
Part C: Short Answer
Answer each question in one or two complete sentences.
1. Why does 0.25 equal twenty-five hundredths?
Sample answer: The 2 sits in the tenths place, worth 0.20 or 20 hundredths, and the 5 sits in the hundredths place, worth 5 hundredths. Together they make 25 hundredths, written 0.25 or 25/100.
Grade 4 students read decimals using place value, recognizing that 0.25 represents 25 hundredths or the fraction 25/100.
2. How do place value columns help you subtract 0.75 - 0.40?
Sample answer: Lining up the decimal points puts 7 tenths above 4 tenths and 5 hundredths above 0 hundredths. Subtracting each column gives 3 tenths and 5 hundredths, which is 0.35.
Grade 4 learners use place value alignment so each digit is subtracted from the matching place, producing the correct difference 0.35.