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Mathematics If, 29 - 1 = 30 9 - 1 = 10 14 - 1 = 1

Mathematics 
If,
29 - 1 = 30
9 - 1 = 10
14 - 1 = 15

Based on above logic, can you prove that 
11 - 1 = 10 ? #Mathematics..
Mathematics 
If,
29 - 1 = 30
9 - 1 = 10
14 - 1 = 15

Based on above logic, can you prove that 
11 - 1 = 10 ? #Mathematics..