Mind Maths

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