Page 10 - Math 7

Set

(iv) Infinite sets

Let’s take a set W = {0, 1, 2, 3, 4, 5, ...}. It is the set of whole numbers. This
set is so large that we can never finish counting its elements. It has infinite
number of elements. So, it is an infinite set.

Thus, a set containing infinite number of elements is called an infinite set.
EXERCISE 1.1

General Section -Classwork
1. Let's tick (—) the well-defined collections. Also, list any three members of
well-defined collections.

a) A collection of greater natural numbers. ............................

b) A collection of natural numbers less than 4. ............................
c) A collection of name of English months starting ............................
with 'J' letter.

d) A collection of favourite English months. ............................

2. If A = { 0, 1, 2, 3, 4, 5 } and P = {2, 3, 5, 7}, let's insert the correct symbol ''
or '' in the blanks..

a) 4 .................. A b) 7 .................. A c) 1 .................. P

d) 5 .................. P e) {2, 3, 5, 7}.............. A f) {2, 3, 5} .................. P
3. Let's tell and write the cardinal numbers of these sets as quickly as possible.

a) A = { 2, 3, 5, 7}, n (A) = .................

b) B = { even numbers less than 7 }, n (B) = .................
c) P = { letters of the word 'PUPIL' }, n (P) = .................
d) O = { odd numbers between 3 and 5 }, n (O) = .................

4. Let's tell and write whether these sets are empty, unit, finite, or infinite as
quickly as possible.

a) A = { odd numbers less than 100 } ...................................................
b) B = { odd numbers more than 100 } ...................................................
c) C = { composite number between 1 and 5 } ...................................................
d) D = { prime number between 7 and 10 } ..................................................

Creative section - A
5. a) Define set. Is the collection of 'tall'' students' in a class a set? Why?
b) Write four methods of describing sets. Give one examples of each method.

Vedanta Excel in Mathematics - Book 7 8 Approved by Curriculum Development Centre, Sanothimi, Bhaktapur