125
Rate of work
Textbook: Part 4, lesson 125, pp. 46–48
GoalThe idea of rate of work; the amount of work A = w × t and the rate w = A : t.
New words
rate of work · unumdorlikamount of work · ish hajmipieces per hour · dona/soatcraftsman · usta
Explanation
The work done in one unit of time is called the rate of work. It is written in units such as pieces/hour, kg/min, m/s. For example, if a machine packs 250 boxes in an hour, its rate is 250 boxes/h. The rate is written w, the time t and the whole amount of work A. To find the amount of work we multiply the rate by the time: A = w × t. To find the rate we divide the amount of work by the time: w = A : t.
Worked examples
A machine packs 250 boxes per hour (w = 250 boxes/h). In 6 hours it packs A = 250 × 6 = 1 500 boxes.
A tailor sewed 160 shirts in 20 days. The rate is w = 160 : 20 = 8 shirts/day.
Class activity
“How many in a minute?”: children write words neatly (or jump) for 1 minute. They count the result, find their own rate in words/min (jumps/min) and predict the amount of work for 5 minutes.
Practice
1
A baker bakes 45 loaves per hour. How many loaves does he bake in 8 hours?
360
2
A factory printed 600 books in 12 days. What is its rate in books/day?
50
3
A pump delivers 30 l of water per minute. How many litres does it deliver in 15 minutes?
450
4
A machine made 63 parts in 9 hours. What is its rate in parts/hour?
7