Page 32 - Math 4

Fundamental Operations Fundamental Operations

Unit Fundamental Operations
3

3.1 Addition and Subtraction - Looking back

Classwork - Exercise

Let's investigate the rule of addition and subtraction with 10, 20, 30, ...

10 + 20 = 30 20 + 30 = 50 40 + 50 = 90

10 + 14 = 24 20 + 23 = 43 28 + 40 = 68

30 – 10 = 20 47 – 20 = 27 75 – 40 = 35

1. Let's mentally apply the above tricks. Then, tell and write the answer
as quickly as possible. It is your mental maths!

a) (i) 10 + 30 = (ii) 20 + 40 = (iii) 40 + 10 =

(iv) 50 + 20 = (v) 60 +30 = (vi) 70 + 20 =

b) (i) 10 + 16 = (ii) 20 + 18 = (iii) 14 + 30 =

(iv) 27 + 30 = (v) 40 + 25 = (vi) 36 + 50 =

c) (i) 30 – 20 = (ii) 40 – 10 = (iii) 70 – 30 =

(iv) 60 – 40 = (v) 80 – 50 = (vi) 90 – 20 =

d) (i) 27 – 10 = (ii) 45 – 30 = (iii) 58 – 20 =

(iv) 64 – 40 = (v) 86 – 50 = (vi) 99 – 60 =

Let's investigate some tricks to add or subtract the numbers faster.

4 + 8 + 6 = 10 + 8 = 18 5 + 7 + 13 = 20 + 5 = 25

12 + 16 = (10 + 10) + (2 + 6) = 28 34 + 33 = (30 + 30) + (4 + 3) = 67

24 – 13 = (24 – 10) – 3 = 11 47 – 25 = (47 – 20) – 5 = 22

26 – 12 = (20 – 10) + (6 – 2) = 14 38 – 15 = (30 – 10) + (8 – 5) = 23

vedanta Excel in Mathematics - Book 4 30 Approved by Curriculum Development Centre, Sanothimi, Bhaktapur