134
Problem solving
Textbook: Part 4, lesson 134, pp. 80–81
GoalProblem solving: time, units, percent, schedules, angles.
New words
timetable · jadvalinterval · intervalpercent · foizaverage · o‘rtacha
Explanation
To solve a problem, read it carefully, separate the known from the unknown, then write an expression or an equation. When adding times, add seconds to seconds and minutes to minutes, and carry anything over 60 to the larger unit. Remember that 25% = 1/4. An equilateral triangle has three equal angles.
Worked examples
6:20 + 1 h 50 min = 8:10. 8 min 47 s + 5 min 38 s = 13 min 85 s = 14 min 25 s.
Each angle of an equilateral triangle is 180° : 3 = 60°.
Class activity
“Timetable makers”: children make a train or bus timetable (every 1 h 50 min), choose the first departure and work out the next ones.
Practice
1
An intercity bus leaves every 1 h 50 min. The first left at 6:20. At what time does the next one leave?
8:10
2
Find the sum 8 min 47 s + 5 min 38 s.
14 min 25 s
3
An airport checks 1 000 passengers an hour. How many does it check in one day?
24000
4
An airport has 800 workers and 25% of them were born in autumn. How many were born in autumn?
200
5
Each plane flies 2 times every 3 days. How many flights do 5 planes make in 30 days?
100