Explore · MATH-5B-C10-L01-OPEN
Compute 3.276 + 1.486 using aligned columns.
Singapore Math 5B · Original independent course
Adding Decimals to Thousandths
Watch for: Aligning last digits rather than decimal points.. Explain what the quantities mean before calculating.
Opening task
Prerequisite check
Before instruction · MATH-5B-C10-L01-PREREQ
Add 2.3 and 0.4.
Show worked answer (after attempting)
Answer: 2.7
Three tenths plus four tenths is seven tenths.
Understand the idea
Add decimals to thousandths by aligning equal place values, with regrouping and realistic contexts. The essential earlier idea is: Chapter 9 decimal place value and 5A regrouping.. The model below will always use the actual quantities from the worked problem. Check aligning last digits rather than decimal points when you explain your answer.
Three worked examples
Worked example 1 · MATH-5B-C10-L01-Q01
Compute 3.275 + 1.486 using aligned columns.
Solution: 4.761
Align decimal places including zero placeholders. 3.275 + 1.486 = 4.761. Inverse check: 4.761 − 1.486 = 3.275.
Worked example 2 · MATH-5B-C10-L01-Q02
Two lengths are 8.04 m and 2.875 m. What is the total?
Solution: 10.915 m
Align decimal places including zero placeholders. 8.04 + 2.875 = 10.915. Inverse check: 10.915 − 2.875 = 8.04.
Worked example 3 · MATH-5B-C10-L01-Q03
Check 6.5 + 0.708 with the inverse operation.
Solution: 7.208
Align decimal places including zero placeholders. 6.5 + 0.708 = 7.208. Inverse check: 7.208 − 0.708 = 6.5.
Check understanding
1 · MATH-5B-C10-L01-Q04
Compute 3.276 + 1.486 using aligned columns.
Show worked answer (after attempting)
Answer: 4.762
Align decimal places including zero placeholders. 3.276 + 1.486 = 4.762. Inverse check: 4.762 − 1.486 = 3.276.
2 · MATH-5B-C10-L01-Q05
Two lengths are 8.041 m and 2.875 m. What is the total?
Show worked answer (after attempting)
Answer: 10.916 m
Align decimal places including zero placeholders. 8.041 + 2.875 = 10.916. Inverse check: 10.916 − 2.875 = 8.041.
3 · MATH-5B-C10-L01-Q06
Check 6.501 + 0.708 with the inverse operation.
Show worked answer (after attempting)
Answer: 7.209
Align decimal places including zero placeholders. 6.501 + 0.708 = 7.209. Inverse check: 7.209 − 0.708 = 6.501.
Guided practice
1 · MATH-5B-C10-L01-Q07
Compute 3.277 + 1.486 using aligned columns.
Show worked answer (after attempting)
Answer: 4.763
Align decimal places including zero placeholders. 3.277 + 1.486 = 4.763. Inverse check: 4.763 − 1.486 = 3.277.
2 · MATH-5B-C10-L01-Q08
Two lengths are 8.042 m and 2.875 m. What is the total?
Show worked answer (after attempting)
Answer: 10.917 m
Align decimal places including zero placeholders. 8.042 + 2.875 = 10.917. Inverse check: 10.917 − 2.875 = 8.042.
3 · MATH-5B-C10-L01-Q09
Check 6.502 + 0.708 with the inverse operation.
Show worked answer (after attempting)
Answer: 7.21
Align decimal places including zero placeholders. 6.502 + 0.708 = 7.21. Inverse check: 7.21 − 0.708 = 6.502.
4 · MATH-5B-C10-L01-Q10
Compute 3.278 + 1.486 using aligned columns.
Show worked answer (after attempting)
Answer: 4.764
Align decimal places including zero placeholders. 3.278 + 1.486 = 4.764. Inverse check: 4.764 − 1.486 = 3.278.
Independent practice
1 · MATH-5B-C10-L01-Q11
Two lengths are 8.043 m and 2.875 m. What is the total?
Show worked answer (after attempting)
Answer: 10.918 m
Align decimal places including zero placeholders. 8.043 + 2.875 = 10.918. Inverse check: 10.918 − 2.875 = 8.043.
2 · MATH-5B-C10-L01-Q12
Check 6.503 + 0.708 with the inverse operation.
Show worked answer (after attempting)
Answer: 7.211
Align decimal places including zero placeholders. 6.503 + 0.708 = 7.211. Inverse check: 7.211 − 0.708 = 6.503.
3 · MATH-5B-C10-L01-Q13
Compute 3.279 + 1.486 using aligned columns.
Show worked answer (after attempting)
Answer: 4.765
Align decimal places including zero placeholders. 3.279 + 1.486 = 4.765. Inverse check: 4.765 − 1.486 = 3.279.
4 · MATH-5B-C10-L01-Q14
Two lengths are 8.044 m and 2.875 m. What is the total?
Show worked answer (after attempting)
Answer: 10.919 m
Align decimal places including zero placeholders. 8.044 + 2.875 = 10.919. Inverse check: 10.919 − 2.875 = 8.044.
5 · MATH-5B-C10-L01-Q15
Check 6.504 + 0.708 with the inverse operation.
Show worked answer (after attempting)
Answer: 7.212
Align decimal places including zero placeholders. 6.504 + 0.708 = 7.212. Inverse check: 7.212 − 0.708 = 6.504.
6 · MATH-5B-C10-L01-Q16
Compute 3.28 + 1.486 using aligned columns.
Show worked answer (after attempting)
Answer: 4.766
Align decimal places including zero placeholders. 3.28 + 1.486 = 4.766. Inverse check: 4.766 − 1.486 = 3.28.
7 · MATH-5B-C10-L01-Q17
Two lengths are 8.045 m and 2.875 m. What is the total?
Show worked answer (after attempting)
Answer: 10.92 m
Align decimal places including zero placeholders. 8.045 + 2.875 = 10.92. Inverse check: 10.92 − 2.875 = 8.045.
8 · MATH-5B-C10-L01-Q18
Check 6.505 + 0.708 with the inverse operation.
Show worked answer (after attempting)
Answer: 7.213
Align decimal places including zero placeholders. 6.505 + 0.708 = 7.213. Inverse check: 7.213 − 0.708 = 6.505.
Challenge and error analysis
1 · MATH-5B-C10-L01-ERR1
The assigned question is: “Two lengths are 8.048 m and 2.875 m. What is the total?” A learner wrote: “8.048 + 2.875 = 11.023. I used this intermediate value to finish the assigned problem.” Identify a concrete invalid step or assumption. Work out the correct result and explain why it is valid.
Show worked answer (after attempting)
Answer: Correct result: 10.923 m
The attempted reasoning or reported result does not satisfy the specified operation, units or geometric conditions. Correct mathematical result: 10.923 m. Recompute from the given data: Align decimal places including zero placeholders. 8.048 + 2.875 = 10.923. Inverse check: 10.923 − 2.875 = 8.048.
2 · MATH-5B-C10-L01-ERR2
The assigned question is: “Check 6.508 + 0.708 with the inverse operation.” A learner wrote: “6.508 + 0.708 = 8.216. I used this intermediate value to finish the assigned problem.” Identify a concrete invalid step or assumption. Work out the correct result and explain why it is valid.
Show worked answer (after attempting)
Answer: Correct result: 7.216
The attempted reasoning or reported result does not satisfy the specified operation, units or geometric conditions. Correct mathematical result: 7.216. Recompute from the given data: Align decimal places including zero placeholders. 6.508 + 0.708 = 7.216. Inverse check: 7.216 − 0.708 = 6.508.
Exit check
Exit · MATH-5B-C10-L01-Q19
Compute 3.281 + 1.486 using aligned columns.
Show worked answer (after attempting)
Answer: 4.767
Align decimal places including zero placeholders. 3.281 + 1.486 = 4.767. Inverse check: 4.767 − 1.486 = 3.281.