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Speed · arrival time
P6 · Speed · PSLE Maths
Question
Mei Ling left home for the library at 2.47 p.m. She first cycled 3.6 km at a speed of 12 km/h. Then she walked the remaining 800 m at a speed of 80 m/min. What time did Mei Ling reach the library?
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Hint
First convert km/h to m/min. Then find the time taken for cycling and walking separately. Finally, add the total time to the starting time.
Show the answer and step-by-step explanation
Answer: Arrival time 3.15 p.m.
- Draw distance model — First split the journey into two parts: cycling 3.6 km and walking 800 m. To calculate easily, change all distances to m.
- Convert speed — The cycling speed is 12 km/h. Since 1 h = 60 min, convert it to m/min.
- Cycling time — The cycling distance is 3600 m and the speed is 200 m/min. Time = distance ÷ speed.
- Walking time — The walking distance is 800 m and the speed is 80 m/min. 800 ÷ 80 = 10 min.
- Total time — Add the two times: 18 min + 10 min = 28 min.
- Use a timeline — Add 28 min to 2.47 p.m. Add 13 min to reach 3.00 p.m.; 15 min is left, so the arrival time is 3.15 p.m.. 📌 Key idea: make the units the same, find the time for each part, then add the total time to the starting time.
Method: In speed problems, make the units the same first. Use time = distance ÷ speed for each part, then use a timeline to add the total time to the starting time.
Practice: 3 similar questions
- Raju left home for the park at 8.20 a.m. He first cycled 4.5 km at 15 km/h. Then he walked 500 m at 50 m/min. What time did Raju reach the park?
Answer
8.48 a.m. — 4.5 km = 4500 m; 15 km/h = 15000 m ÷ 60 min = 250 m/min. Cycling time: 4500 ÷ 250 = 18 min. Walking time: 500 ÷ 50 = 10 min. Total time = 18 + 10 = 28 min. 8.20 a.m. + 28 min = 8.48 a.m.
- Siti left school for the community centre at 1.10 p.m. She first cycled 2.4 km at 9 km/h. Then she walked 600 m at 100 m/min. What time did Siti reach the community centre?
Answer
1.32 p.m. — 2.4 km = 2400 m; 9 km/h = 9000 m ÷ 60 min = 150 m/min. Cycling time: 2400 ÷ 150 = 16 min. Walking time: 600 ÷ 100 = 6 min. Total time = 16 + 6 = 22 min. 1.10 p.m. + 22 min = 1.32 p.m.
- Ali left his tuition centre for home at 5.42 p.m. He first took a bus for 7.2 km at an average speed of 24 km/h. After getting off the bus, he walked 900 m at 60 m/min. What time did Ali reach home?
Answer
6.15 p.m. — 7.2 km = 7200 m; 24 km/h = 24000 m ÷ 60 min = 400 m/min. Bus time: 7200 ÷ 400 = 18 min. Walking time: 900 ÷ 60 = 15 min. Total time = 18 + 15 = 33 min. 5.42 p.m. + 18 min = 6.00 p.m.; 15 min is left, so Ali reached home at 6.15 p.m.
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