Explore · MATH-5B-C14-L04-OPEN
A tap adds 2.6 L/min. Find water after 4 minutes.
Singapore Math 5B · Original independent course
Word Problems
Watch for: Confusing a changing total with a fixed per-unit rate.. Explain what the quantities mean before calculating.
Opening task
Prerequisite check
Before instruction · MATH-5B-C14-L04-PREREQ
At 3 L/min, how much water arrives in 5 minutes?
Show worked answer (after attempting)
Answer: 15 L
Rate × time = 3 × 5 = 15 L.
Understand the idea
Interpret rates in varied practical contexts, explaining both arithmetic and unit meaning. The essential earlier idea is: Chapter 14 L01–L03, ratios, whole/decimal operations.. The model below will always use the actual quantities from the worked problem. Check confusing a changing total with a fixed per-unit rate when you explain your answer.
Three worked examples
Worked example 1 · MATH-5B-C14-L04-Q01
A tap adds 2.5 L/min. Find water after 4 minutes.
Solution: 10 L
Use the constant rate only within the described situation: 2.5 L/min × 4 = 10 L.
Worked example 2 · MATH-5B-C14-L04-Q02
Each identical bag uses 3.2 kg of grain. How much for 5 bags?
Solution: 16 kg
Use the constant rate only within the described situation: 3.2 kg/bag × 5 = 16 kg.
Worked example 3 · MATH-5B-C14-L04-Q03
Travel is 1.8 km/h. What is distance in 6 hours?
Solution: 10.8 km
Use the constant rate only within the described situation: 1.8 km/h × 6 = 10.8 km.
Check understanding
1 · MATH-5B-C14-L04-Q04
A tap adds 2.6 L/min. Find water after 4 minutes.
Show worked answer (after attempting)
Answer: 10.4 L
Use the constant rate only within the described situation: 2.6 L/min × 4 = 10.4 L.
2 · MATH-5B-C14-L04-Q05
Each identical bag uses 3.3 kg of grain. How much for 5 bags?
Show worked answer (after attempting)
Answer: 16.5 kg
Use the constant rate only within the described situation: 3.3 kg/bag × 5 = 16.5 kg.
3 · MATH-5B-C14-L04-Q06
Travel is 1.9 km/h. What is distance in 6 hours?
Show worked answer (after attempting)
Answer: 11.4 km
Use the constant rate only within the described situation: 1.9 km/h × 6 = 11.4 km.
Guided practice
1 · MATH-5B-C14-L04-Q07
A tap adds 2.7 L/min. Find water after 4 minutes.
Show worked answer (after attempting)
Answer: 10.8 L
Use the constant rate only within the described situation: 2.7 L/min × 4 = 10.8 L.
2 · MATH-5B-C14-L04-Q08
Each identical bag uses 3.4 kg of grain. How much for 5 bags?
Show worked answer (after attempting)
Answer: 17 kg
Use the constant rate only within the described situation: 3.4 kg/bag × 5 = 17 kg.
3 · MATH-5B-C14-L04-Q09
Travel is 2 km/h. What is distance in 6 hours?
Show worked answer (after attempting)
Answer: 12 km
Use the constant rate only within the described situation: 2 km/h × 6 = 12 km.
4 · MATH-5B-C14-L04-Q10
A tap adds 2.8 L/min. Find water after 4 minutes.
Show worked answer (after attempting)
Answer: 11.2 L
Use the constant rate only within the described situation: 2.8 L/min × 4 = 11.2 L.
Independent practice
1 · MATH-5B-C14-L04-Q11
Each identical bag uses 3.5 kg of grain. How much for 5 bags?
Show worked answer (after attempting)
Answer: 17.5 kg
Use the constant rate only within the described situation: 3.5 kg/bag × 5 = 17.5 kg.
2 · MATH-5B-C14-L04-Q12
Travel is 2.1 km/h. What is distance in 6 hours?
Show worked answer (after attempting)
Answer: 12.6 km
Use the constant rate only within the described situation: 2.1 km/h × 6 = 12.6 km.
3 · MATH-5B-C14-L04-Q13
A tap adds 2.9 L/min. Find water after 4 minutes.
Show worked answer (after attempting)
Answer: 11.6 L
Use the constant rate only within the described situation: 2.9 L/min × 4 = 11.6 L.
4 · MATH-5B-C14-L04-Q14
Each identical bag uses 3.6 kg of grain. How much for 5 bags?
Show worked answer (after attempting)
Answer: 18 kg
Use the constant rate only within the described situation: 3.6 kg/bag × 5 = 18 kg.
5 · MATH-5B-C14-L04-Q15
Travel is 2.2 km/h. What is distance in 6 hours?
Show worked answer (after attempting)
Answer: 13.2 km
Use the constant rate only within the described situation: 2.2 km/h × 6 = 13.2 km.
6 · MATH-5B-C14-L04-Q16
A tap adds 3 L/min. Find water after 4 minutes.
Show worked answer (after attempting)
Answer: 12 L
Use the constant rate only within the described situation: 3 L/min × 4 = 12 L.
7 · MATH-5B-C14-L04-Q17
Each identical bag uses 3.7 kg of grain. How much for 5 bags?
Show worked answer (after attempting)
Answer: 18.5 kg
Use the constant rate only within the described situation: 3.7 kg/bag × 5 = 18.5 kg.
8 · MATH-5B-C14-L04-Q18
Travel is 2.3 km/h. What is distance in 6 hours?
Show worked answer (after attempting)
Answer: 13.8 km
Use the constant rate only within the described situation: 2.3 km/h × 6 = 13.8 km.
Challenge and error analysis
1 · MATH-5B-C14-L04-ERR1
The assigned question is: “Each identical bag uses 4 kg of grain. How much for 5 bags?” A learner wrote: “I treated the constant rate involving 4 as the whole amount rather than amount per unit, and wrote 20.1 kg.” 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: 20 kg
The attempted reasoning or reported result does not satisfy the specified operation, units or geometric conditions. Correct mathematical result: 20 kg. Recompute from the given data: Use the constant rate only within the described situation: 4 kg/bag × 5 = 20 kg.
2 · MATH-5B-C14-L04-ERR2
The assigned question is: “Travel is 2.6 km/h. What is distance in 6 hours?” A learner wrote: “I treated the constant rate involving 2.6 as the whole amount rather than amount per unit, and wrote 16.6 km.” 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: 15.6 km
The attempted reasoning or reported result does not satisfy the specified operation, units or geometric conditions. Correct mathematical result: 15.6 km. Recompute from the given data: Use the constant rate only within the described situation: 2.6 km/h × 6 = 15.6 km.
Exit check
Exit · MATH-5B-C14-L04-Q19
A tap adds 3.1 L/min. Find water after 4 minutes.
Show worked answer (after attempting)
Answer: 12.4 L
Use the constant rate only within the described situation: 3.1 L/min × 4 = 12.4 L.