Square the tens digit and the ones digit and put it on both sides. Double the product of the digits and put it in the middle. If the results have no carry over, these become the digits of the answer.
Below are examples of no carry over.
13 x 13 = ?
1*1 2*1*3 3*3
1 6 9
13 x 13 = 169
12 x 12 = ?
1*1 2*1*2 2*2
1 4 4
12 x 12 = 144
11 x 11 = ?
1*1 2*1*1 1*1
1 2 1
11 x 11 = 121
21 x 21 = ?
2*2 2*2*1 1*1
4 4 1
21 x 21 = 441
41 x 41 = ?
4*4 2*4*1 1*1
16 8 1
41 x 41 = 1681
70 x 70 = ?
7*7 2*7*0 0*0
49 0 0
70 x 70 = 4900
When the results are 2-digit numbers, carry the tens digit to the preceding number.
Below are examples with carry over.
62 x 62 = ?
6*6 2*6*2 2*2
36 24 4
36+2 4 4
38 4 4
62 x 62 = 3844
18 x 18 = ?
1*1 2*1*8 8*8
1 16 64
1+1 6+6 4
2 12 4
2+1 2 4
3 2 4
18 x 18 = 324
15 x 15 = ?
1*1 2*1*5 5*5
1 10 25
1+1 0+2 5
2 2 5
15 x 15 = 225
It seems long to write because I am showing here the step by step process. But this trick takes only seconds in the mind.
#Matamata
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