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:
To add 3.45 + 12.6 in Grade 4, you write 3.45 above 12.6 and align the rightmost digits before adding.
Corrected: To add 3.45 + 12.6 in Grade 4, you align the decimal points and write 12.6 as 12.60 before adding.
Place value matters: tenths align with tenths and hundredths with hundredths.
2. Fix the sentence:
When a Grade 4 student adds 5.7 and 2.34, the sum is wrote as 7.04 because 7 plus 34 equals 41.
Corrected: When a Grade 4 student adds 5.7 and 2.34, the sum is written as 8.04 because 5.70 plus 2.34 equals 8.04.
Adding equivalent decimals keeps place values aligned correctly.
3. Fix the sentence:
In Grade 4, the sum of 0.6 plus 0.45 equal 0.51 when you simply joins the digits together.
Corrected: In Grade 4, the sum of 0.6 plus 0.45 equals 1.05 when you align decimal points and add carefully.
Tenths and hundredths must be added column by column.
Part B: Fill in the Blank
Write the missing word or number on each line.
1. Grade 4: To add 3.45 + 12.6, rewrite 12.6 as 12.60 so the hundredths place is filled.
Adding a trailing zero does not change the value.
2. Grade 4: When stacking 7.8 + 2.35, place the decimal point directly under the other decimal point.
Aligning decimal points keeps place values lined up.
3. Grade 4: The sum 4.27 + 1.5 equals 5.77 after aligning and annexing a zero.
Hundredths column adds 7 + 0 = 7.
4. Grade 4: Adding 0.9 + 0.08 gives 0.98 because tenths and hundredths must be aligned.
Nine tenths plus eight hundredths totals ninety-eight hundredths.
Part C: Short Answer
Answer each question in one or two complete sentences.
1. Grade 4: Explain why you must annex a zero when adding 6.4 + 3.27.
Sample answer: You annex a zero so 6.4 becomes 6.40, which gives the same value but fills the hundredths place. This lets you add column by column without confusing tenths and hundredths.
Annexing zeros makes addends have equal decimal places.
2. Grade 4: Describe the steps to add 9.6 + 4.85 vertically.
Sample answer: First write 9.6 as 9.60. Stack 9.60 above 4.85 with decimal points aligned. Add hundredths: 0+5=5. Add tenths: 6+8=14, write 4 carry 1. Add ones: 9+4+1=14. The sum is 14.45.
Column-by-column addition relies on aligned place values.