7
Review: rate-of-work problems
Textbook: Part 1, lesson 7, pp. 22–24
GoalReview the link between rate of work, working time and amount of work.
New words
rate of work · ish unumdorligiamount of work · ish hajmiworking time · ish vaqtishift · smena
Explanation
The amount of work done in one unit of time is the rate of work (v). With amount of work A and working time t: A = v × t, v = A : t, t = A : v. These look like the motion formulas: the rate of work takes the place of speed and the amount of work the place of distance.
Worked examples
A machine makes 160 parts per hour. In 6 hours it makes 160 × 6 = 960 parts.
24 000 boxes were packed in a shift at 3 000 boxes per hour. The shift lasted 24 000 : 3 000 = 8 hours.
Class activity
“Workshop”: each group of “craftspeople” gets an amount of work and a time (for example, 60 paper flowers in 5 minutes). They work out the rate and decide which group works faster.
Practice
1
A machine makes 240 parts per hour. How many parts does it make in 7 hours?
1680
2
A factory made 5 400 bricks in 6 hours. How many bricks per hour is that?
900
3
A tailor sews 12 shirts a day. In how many days will she sew 96 shirts?
8
4
The first craftsman made 48 parts in 4 hours, the second 55 parts in 5 hours. Whose rate of work is higher?
The first: 12 per hour > 11 per hour