103
The 3 times table
Textbook: Part 3, lesson 97, pp. 54–55
GoalKnow the 3 times table; find the perimeter of an equilateral triangle.
New words
the 3 times table · 3 ga ko‘paytirish jadvaliequilateral triangle · teng tomonli uchburchakbroken line (polyline) · siniq chiziqlink, segment of a polyline · bo‘g‘in
Explanation
The 3 times table comes from counting in threes: 3, 6, 9, 12, 15, 18, 21, 24, 27, 30. A triangle whose sides are all equal is called equilateral. Its perimeter is the side times 3: P = a × 3. If all links of a broken line are equal, its length is the link length times the number of links.
Worked examples
3 × 4 = 12 and 8 × 3 = 24.
An equilateral triangle with side 6 cm has perimeter 6 × 3 = 18 cm.
Class activity
“Jump in threes”: children hop along a number line in steps of 3, saying the table aloud at each jump.
Practice
1
3 × 7 = ?
21
2
9 × 3 = ?
27
3
An equilateral triangle has side 6 cm. What is its perimeter in cm?
18
4
A broken line has 4 links of 3 cm each. How long is it in cm?
12
5
Each volunteer brought 3 toys. How many toys did 5 volunteers bring?
15