RATE AND SPEED

Rate

A factory worker is paid \$64 for working 8 hours.

For 1 hour, he is paid \$64
8
= \$8.

He is paid the rate of \$8 per hour.

Example:

A typist types at the rate of 45 words per minute. How long will she take to type 3 sheets of notes if there are 180 words in each sheet of paper?

Number of words on 1 sheet of paper = 180

Number of words on 3 sheets of paper = 180 x 3
= 540

Typing rate = 45 words per minute

Time taken to type 540 words = 540
45
= 12 minutes

She will take 12 minutes to type 3 sheets of notes.

Speed

When a motorist travels 75 kilometres in l hour, we say that he is travelling at a speed of 75 km/h.

Average speed = Distance
Time

Distance travelled = Speed x Time

Time taken = Distance
Speed

Examples:

1. A car travelled at an average speed of 65 km/h for 2 ½ hours. How far did it travel?

 Distance Time Speed (a) 2 ½ h 65 km/h

Time taken to travel = 2 ½ h

Average speed = 65 km/h

Total distatance travelled = 2 ½ x 65

= 5/2 x 65

= 325
2

= 162 ½ km or 162.5 km …………………. (a)

2. At an average speed of 75 km/h, how long will it take a car to travel 300 km?

 Distance Time Speed 300 km (a) 75 km/h

Total distance travelled = 300 km

Average speed = 75 km/h

Time taken to travel 300 km = 370
75
= 4h ……………………….. (a)

3. A van travelled 288 km in 6 hours. Find its average speed in km/h.

 Distance Time Speed 288 km 6 h (a)

Total distance travelled = 288 km

Total time taken = 6 h

Average speed of van = 288
6
= 48 km/h ……………………......... (a)

4. Mr Johari took 2 hours to drive from Town X to Town Y at an average speed of 50 km/h. He took another 2 1/2 hours to drive from Town Y to Town Z at an average speed of 60 km/h. Find the total distance travelled by Mr Johari.

 Event Distance Time Speed X --> Y Y --> Z Total (a) (b) (c) 2 h 2 ½ h 50 km/h 60 km/h

Distance from X to Y = 2 x 50
= 100 km …………………..............................……(a)

Distance from Y to Z = 2 1/2 x 60
= 150 km …………....................................………. (b)

Total distance travelled = 100 + 150
= 250 km……………......................................…… (c)