Explore · MATH-5B-C10-L02-OPEN
Compute 3.276 − 1.486 using aligned columns.
Singapore Math 5B · Original independent course
Subtracting Decimals
Watch for: Subtracting a larger digit from a smaller without regrouping.. Explain what the quantities mean before calculating.
Opening task
Prerequisite check
Before instruction · MATH-5B-C10-L02-PREREQ
Compute 5.0 − 2.6.
Show worked answer (after attempting)
Answer: 2.4
Subtract aligned tenths: 5.0 − 2.6 = 2.4.
Understand the idea
Subtract decimals with aligned place values and exchanges across zeros, verifying by addition. The essential earlier idea is: Chapter 9 decimal place value and subtraction algorithm.. The model below will always use the actual quantities from the worked problem. Check subtracting a larger digit from a smaller without regrouping when you explain your answer.
Three worked examples
Worked example 1 · MATH-5B-C10-L02-Q01
Compute 3.275 − 1.486 using aligned columns.
Solution: 1.789
Align decimal places including zero placeholders. 3.275 − 1.486 = 1.789. Inverse check: 1.789 + 1.486 = 3.275.
Worked example 2 · MATH-5B-C10-L02-Q02
Two lengths are 8.04 m and 2.875 m. How much longer is the first?
Solution: 5.165 m
Align decimal places including zero placeholders. 8.04 − 2.875 = 5.165. Inverse check: 5.165 + 2.875 = 8.04.
Worked example 3 · MATH-5B-C10-L02-Q03
Check 6.5 − 0.708 with the inverse operation.
Solution: 5.792
Align decimal places including zero placeholders. 6.5 − 0.708 = 5.792. Inverse check: 5.792 + 0.708 = 6.5.
Check understanding
1 · MATH-5B-C10-L02-Q04
Compute 3.276 − 1.486 using aligned columns.
Show worked answer (after attempting)
Answer: 1.79
Align decimal places including zero placeholders. 3.276 − 1.486 = 1.79. Inverse check: 1.79 + 1.486 = 3.276.
2 · MATH-5B-C10-L02-Q05
Two lengths are 8.041 m and 2.875 m. How much longer is the first?
Show worked answer (after attempting)
Answer: 5.166 m
Align decimal places including zero placeholders. 8.041 − 2.875 = 5.166. Inverse check: 5.166 + 2.875 = 8.041.
3 · MATH-5B-C10-L02-Q06
Check 6.501 − 0.708 with the inverse operation.
Show worked answer (after attempting)
Answer: 5.793
Align decimal places including zero placeholders. 6.501 − 0.708 = 5.793. Inverse check: 5.793 + 0.708 = 6.501.
Guided practice
1 · MATH-5B-C10-L02-Q07
Compute 3.277 − 1.486 using aligned columns.
Show worked answer (after attempting)
Answer: 1.791
Align decimal places including zero placeholders. 3.277 − 1.486 = 1.791. Inverse check: 1.791 + 1.486 = 3.277.
2 · MATH-5B-C10-L02-Q08
Two lengths are 8.042 m and 2.875 m. How much longer is the first?
Show worked answer (after attempting)
Answer: 5.167 m
Align decimal places including zero placeholders. 8.042 − 2.875 = 5.167. Inverse check: 5.167 + 2.875 = 8.042.
3 · MATH-5B-C10-L02-Q09
Check 6.502 − 0.708 with the inverse operation.
Show worked answer (after attempting)
Answer: 5.794
Align decimal places including zero placeholders. 6.502 − 0.708 = 5.794. Inverse check: 5.794 + 0.708 = 6.502.
4 · MATH-5B-C10-L02-Q10
Compute 3.278 − 1.486 using aligned columns.
Show worked answer (after attempting)
Answer: 1.792
Align decimal places including zero placeholders. 3.278 − 1.486 = 1.792. Inverse check: 1.792 + 1.486 = 3.278.
Independent practice
1 · MATH-5B-C10-L02-Q11
Two lengths are 8.043 m and 2.875 m. How much longer is the first?
Show worked answer (after attempting)
Answer: 5.168 m
Align decimal places including zero placeholders. 8.043 − 2.875 = 5.168. Inverse check: 5.168 + 2.875 = 8.043.
2 · MATH-5B-C10-L02-Q12
Check 6.503 − 0.708 with the inverse operation.
Show worked answer (after attempting)
Answer: 5.795
Align decimal places including zero placeholders. 6.503 − 0.708 = 5.795. Inverse check: 5.795 + 0.708 = 6.503.
3 · MATH-5B-C10-L02-Q13
Compute 3.279 − 1.486 using aligned columns.
Show worked answer (after attempting)
Answer: 1.793
Align decimal places including zero placeholders. 3.279 − 1.486 = 1.793. Inverse check: 1.793 + 1.486 = 3.279.
4 · MATH-5B-C10-L02-Q14
Two lengths are 8.044 m and 2.875 m. How much longer is the first?
Show worked answer (after attempting)
Answer: 5.169 m
Align decimal places including zero placeholders. 8.044 − 2.875 = 5.169. Inverse check: 5.169 + 2.875 = 8.044.
5 · MATH-5B-C10-L02-Q15
Check 6.504 − 0.708 with the inverse operation.
Show worked answer (after attempting)
Answer: 5.796
Align decimal places including zero placeholders. 6.504 − 0.708 = 5.796. Inverse check: 5.796 + 0.708 = 6.504.
6 · MATH-5B-C10-L02-Q16
Compute 3.28 − 1.486 using aligned columns.
Show worked answer (after attempting)
Answer: 1.794
Align decimal places including zero placeholders. 3.28 − 1.486 = 1.794. Inverse check: 1.794 + 1.486 = 3.28.
7 · MATH-5B-C10-L02-Q17
Two lengths are 8.045 m and 2.875 m. How much longer is the first?
Show worked answer (after attempting)
Answer: 5.17 m
Align decimal places including zero placeholders. 8.045 − 2.875 = 5.17. Inverse check: 5.17 + 2.875 = 8.045.
8 · MATH-5B-C10-L02-Q18
Check 6.505 − 0.708 with the inverse operation.
Show worked answer (after attempting)
Answer: 5.797
Align decimal places including zero placeholders. 6.505 − 0.708 = 5.797. Inverse check: 5.797 + 0.708 = 6.505.
Challenge and error analysis
1 · MATH-5B-C10-L02-ERR1
The assigned question is: “Two lengths are 8.048 m and 2.875 m. How much longer is the first?” A learner wrote: “8.048 − 2.875 = 5.273. 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: 5.173 m
The attempted reasoning or reported result does not satisfy the specified operation, units or geometric conditions. Correct mathematical result: 5.173 m. Recompute from the given data: Align decimal places including zero placeholders. 8.048 − 2.875 = 5.173. Inverse check: 5.173 + 2.875 = 8.048.
2 · MATH-5B-C10-L02-ERR2
The assigned question is: “Check 6.508 − 0.708 with the inverse operation.” A learner wrote: “6.508 − 0.708 = 6.8. 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: 5.8
The attempted reasoning or reported result does not satisfy the specified operation, units or geometric conditions. Correct mathematical result: 5.8. Recompute from the given data: Align decimal places including zero placeholders. 6.508 − 0.708 = 5.8. Inverse check: 5.8 + 0.708 = 6.508.
Exit check
Exit · MATH-5B-C10-L02-Q19
Compute 3.281 − 1.486 using aligned columns.
Show worked answer (after attempting)
Answer: 1.795
Align decimal places including zero placeholders. 3.281 − 1.486 = 1.795. Inverse check: 1.795 + 1.486 = 3.281.