128
Sets
Textbook: Part 4, lesson 128, pp. 57–59
GoalThe ideas of a set and an element; writing a set by listing its elements or by stating a common property.
New words
set · to‘plamelement · elementcurly brackets · figurali qavscommon name · umumiy nom
Explanation
A group of objects that share some property is called a set: the set of birds, the set of numbers, the set of shapes. Each object in a set is called its element. A set is named with a capital Latin letter: A, B, C. A set can be written in two ways: by listing its elements in curly brackets, for example A = {1, 2, 3}, or by stating the common property: A is the set of natural numbers less than 4.
Worked examples
H is the set of days of the week: H = {Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday}. It has 7 elements.
B is the set of natural numbers less than 5. Listing the elements: B = {1, 2, 3, 4}.
Class activity
“Let us make sets”: each child gets a picture card (animal, fruit, shape, number). Children join groups by a common property and name their set.
Practice
1
Write the set of one-digit odd numbers by listing its elements.
{1, 3, 5, 7, 9}
2
Write the set of traffic-light colours by listing its elements.
{red, yellow, green}
3
Give a common name to the set whose elements are apple, pear, quince, grape.
The set of fruits
4
Write the set of natural numbers less than 20 that are multiples of 5.
{5, 10, 15}
5
How many elements does the set of working days (Monday–Friday) have?
5