Squaring numbers in the 70s
 Square the last digit (keep the carry) _ _ _ X
 Multiply the last digit by 14, add the carry _ _ X _
 The first digits will be 49 plus the carry: X X _ _
Example:
If the number to be squared is 72:
 Square the last digit:
2 × 2 = 4 _ _ _ 4
 Multiply the last digit by 14:
14 × 2 = 28 (keep the carry) _ _ 8 _
 The first digits will be 49 plus the carry:
49 (+ carry): 49 + 2 = 51 5 1 _ _
 So 72 × 72 = 5184.
See the pattern?
If the number to be squared is 78:
 Square the last digit (keep the carry):
8 × 8 = 64 (keep 6) _ _ _ 4
 Multiply the last digit by 14, add the carry:
14 × 8 = 80 + 32 = 112
112 + 6 = 118 (keep 11) _ _ 8 _
 The first digits will be 49 plus the carry (11):
49 (+ carry): 49 + 11 = 60 6 0 _ _.
 So 78 × 78 = 6084.
