FINDING CUBE OF NUMBERS
NUMBERS BETWEEN 10-20
Students should remember cubes of 10 numbers.
13 = 1
23 = 8
33 = 27
43 = 64
53 = 125
63 = 216
73 = 343
83 = 512
93 = 729
103 = 1000
We take an example and understand this method.
Let us find the cube of 13 –
First write two digits of 13 in the first 2 places
Write square of 2nd digit (here 3) in the third place and cube of 2nd digit in the fourth place
1 3 9 27
Double the middle numbers and add
1 3 9 27
6 18
(1) (2) (2)
2 1 9 7
∴ 133 = 2197
Let us find the cube of 15 –
Square of 5 = 25; cube of 5 = 125
1 5 25 125
Double the middle numbers and add
1 5 25 125
10 50
(2) (8) (12)
3 3 7 5
∴153 = 2197
Similarly,
Cube of 18 –
1 8 64 512
Double the middle numbers and add
1 8 64 512
16 128
(4) (24) (51)
5 8 3 2
∴ 183 = 5832