Average speed worksheet

Part A: Working out and filling in

1. 1. Average speed = 35 km/h

   Average speed = total distance ÷ total time: there takes 105 ÷ 21 = 5 h, back takes 105 ÷ 105 = 1 h, there and back is 105 × 2 = 210 km, total time 5 + 1 = 6 h, 210 ÷ 6 = 35 km/h (not (21 + 105) ÷ 2 = 63: the slower way takes longer)

2. 2. Average speed = 135 m/min

   Average speed = total distance ÷ total time: there takes 1620 ÷ 108 = 15 min, back takes 1620 ÷ 180 = 9 min, there and back is 1620 × 2 = 3240 m, total time 15 + 9 = 24 min, 3240 ÷ 24 = 135 m/min (not (108 + 180) ÷ 2 = 144: the slower way takes longer)

3. 3. Average speed = 24 km/h

   Average speed = total distance ÷ total time: there takes 84 ÷ 28 = 3 h, back takes 84 ÷ 21 = 4 h, there and back is 84 × 2 = 168 km, total time 3 + 4 = 7 h, 168 ÷ 7 = 24 km/h (not the mean of the two speeds: the slower way takes longer)

4. 4. Average speed = 38 km/h

   Average speed = total distance ÷ total time: total distance 144 + 160 = 304 km, total time 4 + 4 = 8 h, 304 ÷ 8 = 38 km/h

5. 5. Average speed = 76 km/h

   Average speed = total distance ÷ total time: leg 2 is 60 × 3 = 180 km, total distance 200 + 180 = 380 km, total time 2 + 3 = 5 h, 380 ÷ 5 = 76 km/h

6. 6. Average speed = 64 km/h

   Average speed = total distance ÷ total time: there and back is 192 × 2 = 384 km, total time 4 + 2 = 6 h, 384 ÷ 6 = 64 km/h

7. 7. Average speed = 64 km/h

   Average speed = total distance ÷ total time: leg 2 is 72 × 1 = 72 km, total distance 120 + 72 = 192 km, total time 2 + 1 = 3 h, 192 ÷ 3 = 64 km/h

8. 8. Average speed = 35 km/h

   Average speed = total distance ÷ total time: there and back is 105 × 2 = 210 km, total time 1 + 5 = 6 h, 210 ÷ 6 = 35 km/h

9. 9. Average speed = 60 km/h

   Average speed = total distance ÷ total time: leg 1 is 30 × 2 = 60 km, total distance 60 + 180 = 240 km, total time 2 + 2 = 4 h, 240 ÷ 4 = 60 km/h

10. 10. Average speed = 84 km/h

    Average speed = total distance ÷ total time: leg 2 is 100 × 5 = 500 km, total distance 256 + 500 = 756 km, total time 4 + 5 = 9 h, 756 ÷ 9 = 84 km/h

11. 11. Average speed = 120 m/min

    Average speed = total distance ÷ total time: total distance 1200 + 480 = 1680 m, total time 8 + 6 = 14 min, 1680 ÷ 14 = 120 m/min

12. 12. Average speed = 52 km/h

    Average speed = total distance ÷ total time: total distance 200 + 216 = 416 km, total time 4 + 4 = 8 h, 416 ÷ 8 = 52 km/h

Part B: Word problems

Marking: 2 for the working, 1 for the answer, 1 for the sentence.

1. 13. Tsz-hin's family drive to the countryside, first at 40 km/h for 2 h, then at 80 km/h for 3 h. What is their average speed for the whole trip, in km/h? (Answer: 64 km/h)

   40 × 2 + 80 × 3 = 320; 2 + 3 = 5; 320 ÷ 5 = 64

2. 14. Tsz-ching walks 800 m in 7 minutes, then runs 1200 m in 3 minutes. What is her average speed for the whole distance, in m/min? (Answer: 200 m/min)

   800 + 1200 = 2000; 7 + 3 = 10; 2000 ÷ 10 = 200

3. 15. Ka-yee walks 600 m in 5 minutes, then runs 1500 m in 5 minutes. What is her average speed for the whole distance, in m/min? (Answer: 210 m/min)

   600 + 1500 = 2100; 5 + 5 = 10; 2100 ÷ 10 = 210

4. 16. Ming's family drive to the countryside, first at 60 km/h for 1 h, then at 80 km/h for 1 h. What is their average speed for the whole trip, in km/h? (Answer: 70 km/h)

   60 × 1 + 80 × 1 = 140; 1 + 1 = 2; 140 ÷ 2 = 70

5. 17. A van drives 30 km from a warehouse to a shopping centre. It takes 1 h there and 4 h back. What is its average speed for the round trip, in km/h? (Answer: 12 km/h)

   30 × 2 = 60; 1 + 4 = 5; 60 ÷ 5 = 12

6. 18. A van drives 100 km from a warehouse to a shopping centre. It takes 3 h there and 1 h back. What is its average speed for the round trip, in km/h? (Answer: 50 km/h)

   100 × 2 = 200; 3 + 1 = 4; 200 ÷ 4 = 50