126
Solving rate-of-work problems
Textbook: Part 4, lesson 126, pp. 49–51
GoalRate-of-work problems: finding the time t = A : w and the work of two workers (teams).
New words
working time · ish vaqtiteam · brigadatogether · birgalikdatable · jadval
Explanation
If the amount of work A and the rate w are known, we find the time with t = A : w. If two workers or teams work at the same time, we add their rates, or find each amount of work and then add. Writing the condition in a table with columns w, t, A helps us understand the problem.
Worked examples
A printer prints 20 pages per minute. To print 160 pages it needs t = 160 : 20 = 8 minutes.
The first team lays 45 m of pipe per day, the second 35 m. In 5 days together they lay (45 + 35) × 5 = 80 × 5 = 400 m.
Class activity
“Teams”: the class splits into two teams. Each team measures how many shapes (for example squares) it can draw in 1 minute. They record it in a table and calculate how many shapes they draw together in 5 minutes.
Practice
1
A tailor sews 6 shirts per hour. In how many hours does she sew 54 shirts?
9
2
12 l of water flows from a pipe each minute. In how many minutes is a 300 l tank filled?
25
3
The first team builds 150 m of road per day and the second 130 m. How many metres do they build together in 4 days?
1120
4
Laylo knits 5 napkins per hour. Can she knit 18 napkins from 9:00 to 12:00?
No: in 3 hours she knits 5 × 3 = 15, which is less than 18.